Batteries In A Portable Wold
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> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
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Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 6 > Chapter 8 > Chapter 9 > Chapter 15 > Chapter 4 > Chapter 5
> Chapter 7 > Chapter 10 > Chapter 12 > Chapter 16 > Chapter 11 > Chapter 13 > Neue Artikel > Articulos Nuevos > Articles Nouveaux > Werden
Lithium-Ion Akkus sich im neuen Millennium behaupten? > ¿Las baterías de Litio-Ion energizaran el nuevo milenio? > Was begrenzt die Betriebszeit eines
Akkus? > El secreto del tiempo de duración en las baterías > Welcher Akku hält länger? > Akku-Geheimnis gelöst! > Table of Contents > Author's Note
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Author's Note
Battery user groups have asked me to write an edited version of Batteries in a
Portable World. The first edition was published in 1997. Much has changed
since then.
My very first publication in book form was entitled Strengthening the
Weakest Link. It was, in part, a collection of battery articles which I had
written. These articles had been published in various trade magazines and
gained the interest of many readers. This goes back to the late 1980s and the
material covered topics such as the memory effect of NiCd batteries and how
to restore them.
In the early 1990s, attention moved to the nickel-metal hydride (NiMH) and
the articles compared the classic nickel cadmium (NiCd) with the NiMH, the
new kid on the block. In terms of longevity and ruggedness, the NiMH did not
perform so well when placed against the NiCd and I was rather blunt about it.
Over the years, however, the NiMH improved and today this chemistry
performs well for mobile phones and other applications.
Then came the lithium-ion (Liion), followed by the lithium-ion polymer (Li
ion polymer). Each of these new systems, as introduced, claimed better
performance, freedom from the memory effect and longer runtimes than the
dated NiCd. In many cases, the statements made by the manufacturers about
improvements were true, but not all users were convinced.
The second edition of Batteries in a Portable World has grown to more than
three times the size of the previous version. It describes the battery in a
broader scope and includes the latest technologies, such as battery quick test.
Some new articles have also been woven in and some redundancies cannot be
fully avoided. Much of this fresh material has been published in trade
magazines, both in North America and abroad.
In the battery field, there is no black and white, but many shades of gray. In
fact, the battery behaves much like a human being. It is mystical,
unexplainable and can never be fully understood. For some users, the battery
causes no problems at all, for others it is nothing but a problem. Perhaps a
comparison can be made with the aspirin. For some, it works to remedy a
headache, for others the headache gets worse. And no one knows exactly why.
Batteries in a Portable World is written for the non-engineer. It addresses the
use of the battery in the hands of the general public, far removed from the
protected test lab environment of the manufacturer. Some information
contained in this book was obtained through tests performed in Cadex
laboratories; other knowledge was gathered by simply talking to diverse
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groups of battery users. Not all views and opinions expressed in the book are
based on scientific facts. Rather, they follow opinions of the general public,
who use batteries. Some difference of opinion with the reader cannot be
avoided. I will accept the blame for any discrepancies, if justified.
Readers of the previous edition have commented that I favor the NiCd over
the NiMH. Perhaps this observation is valid and I have taken note. Having
been active in the mobile radio industry for many years, much emphasis was
placed on the longevity of a battery, a quality that is true of the NiCd. Today’s
battery has almost become a disposable item. This is especially true in the
vast mobile phone market where small size and high energy density take
precedence over longevity.
Manufacturers are very much in tune with customers’ demands and deliver on
maximum runtime and small size. These attributes are truly visible at the sales
counter and catch the eye of the vigilant buyer. What is less evident is the
shorter service life. However, with rapidly changing technology, portable
equipment is often obsolete by the time the battery is worn out. No longer do
we need to pamper a battery like a Stradivarius violin that is being handed
down from generation to generation. With mobile phones, for example,
upgrading to a new handset may be cheaper than purchasing a replacement
battery. Small size and reasonable runtime are key issues that drive the
consumer market today. Longevity often comes second or third.
In the industrial market such as public safety, biomedical, aviation and
defense, requirements are different. Longevity is given preference over small
size. To suit particular applications, battery manufacturers are able to adjust
the amount of chemicals and active materials that go into a cell. This
fine-tuning is done on nickel-based as well as lead and lithium-based
batteries.
In a nutshell, the user is given the choice of long runtime, small size or high
cycle count. No one single battery can possess all these attributes. Battery
technology is truly a compromise.
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Copyright 2001 Isidor Buchmann. All rights reserved.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 6 > Chapter 8 > Chapter 9 > Chapter 15 > Chapter 4 > Chapter 5
> Chapter 7 > Chapter 10 > Chapter 12 > Chapter 16 > Chapter 11 > Chapter 13 > Neue Artikel > Articulos Nuevos > Articles Nouveaux > Werden
Lithium-Ion Akkus sich im neuen Millennium behaupten? > ¿Las baterías de Litio-Ion energizaran el nuevo milenio? > Was begrenzt die Betriebszeit eines
Akkus? > El secreto del tiempo de duración en las baterías > Welcher Akku hält länger? > Akku-Geheimnis gelöst! > Table of Contents > Author's Note >
Introduction
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Introduction
During the last few decades, rechargeable batteries have made only moderate
improvements in terms of higher capacity and smaller size. Compared with
the vast advancements in areas such as microelectronics, the lack of progress
in battery technology is apparent. Consider a computer memory core of the
sixties and compare it with a modern microchip of the same byte count. What
once measured a cubic foot now sits in a tiny chip. A comparable size
reduction would literally shrink a heavy-duty car battery to the size of a coin.
Since batteries are still based on an electrochemical process, a car battery the
size of a coin may not be possible using our current techniques.
Research has brought about a variety of battery chemistries, each offering
distinct advantages but none providing a fully satisfactory solution. With
today’s increased selection, however, better choices can be applied to suit a
specific user application.
The consumer market, for example, demands high energy densities and small
sizes. This is done to maintain adequate runtime on portable devices that are
becoming increasingly more powerful and power hungry. Relentless
downsizing of portable equipment has pressured manufacturers to invent
smaller batteries. This, however, must be done without sacrificing runtimes.
By packing more energy into a pack, other qualities are often compromised.
One of these is longevity.
Long service life and predictable low internal resistance are found in the NiCd
family. However, this chemistry is being replaced, where applicable, with
systems that provide longer runtimes. In addition, negative publicity about the
memory phenomenon and concerns of toxicity in disposal are causing
equipment manufacturers to seek alternatives.
Once hailed as a superior battery system, the NiMH has also failed to provide
the universal battery solution for the twenty-first century. Shorter than
expected service life remains a major complaint.
The lithium-based battery may be the best choice, especially for the
fast-moving commercial market. Maintenance-free and dependable, Li-ion is
the preferred choice for many because it offers small size and long runtime.
But this battery system is not without problems. A relatively rapid aging
process, even if the battery is not in use, limits the life to between two and
three years. In addition, a current-limiting safety circuit limits the discharge
current, rendering the Li-ion unsuitable for applications requiring a heavy
load. The Li-ion polymer exhibits similar characteristics to the Li-ion. No
major breakthrough has been achieved with this system. It does offer a very
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slim form factor but this quality is attained in exchange for slightly less
energy density.
With rapid developments in technology occurring today, battery systems that
use neither nickel, lead nor lithium may soon become viable. Fuel cells, which
enable uninterrupted operation by drawing on a continuous supply of fuel,
may solve the portable energy needs in the future. Instead of a charger, the
user carries a bottle of liquid energy. Such a battery would truly change the
way we live and work.
This book addresses the most commonly used consumer and industrial
batteries, which are NiCd, NiMH, Lead Acid, and Li-ion/polymer. It also
includes the reusable alkaline for comparison. The absence of other
rechargeable battery systems is done for reasons of clarity. Some weird and
wonderful new battery inventions may only live in experimental labs. Others
may be used for specialty applications, such as military and aerospace. Since
this book addresses the non-engineer, it is the author’s wish to keep the matter
as simple as possible.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 6 > Chapter 8 > Chapter 9 > Chapter 15 > Chapter 4 > Chapter 5
> Chapter 7 > Chapter 10 > Chapter 12 > Chapter 16 > Chapter 11 > Chapter 13 > Neue Artikel > Articulos Nuevos > Articles Nouveaux > Werden
Lithium-Ion Akkus sich im neuen Millennium behaupten? > ¿Las baterías de Litio-Ion energizaran el nuevo milenio? > Was begrenzt die Betriebszeit eines
Akkus? > El secreto del tiempo de duración en las baterías > Welcher Akku hält länger? > Akku-Geheimnis gelöst! > Table of Contents > Author's Note >
Introduction > Chapter 1
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Chapter 1: When was the
battery invented?
One of the most remarkable and novel discoveries in the last 400 years has
been electricity. One may ask, “Has electricity been around that long?” The
answer is yes, and perhaps much longer. But the practical use of electricity
has only been at our disposal since the mid-to late 1800s, and in a limited way
at first. At the world exposition in Paris in 1900, for example, one of the main
attractions was an electrically lit bridge over the river Seine.
The earliest method of generating electricity occurred by creating a static
charge. In 1660, Otto von Guericke constructed the first electrical machine
that consisted of a large sulphur globe which, when rubbed and turned,
attracted feathers and small pieces of paper. Guericke was able to prove that
the sparks generated were truly electrical.
The first suggested use of static electricity was the so-called “electric pistol”.
Invented by Alessandro Volta (1745-1827), an electrical wire was placed in a
jar filled with methane gas. By sending an electrical spark through the wire,
the jar would explode.
Volta then thought of using this invention to provide long distance
communications, albeit only addressing one Boolean bit. An iron wire
supported by wooden poles was to be strung from Como to Milan, Italy. At
the receiving end, the wire would terminate in a jar filled with methane gas.
On command, an electrical spark is sent by wire that would detonate the
electric pistol to signal a coded event. This communications link was
never built.
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Figure 1-1:
Alessandro Volta, inventor of the electric battery.
Volta’s discovery of the decomposition of water by an electrical current laid
the foundation of electrochemistry. ©Cadex Electronics Inc.
In 1791, while working at Bologna University, Luigi Galvani discovered that
the muscle of a frog contracted when touched by a metallic object. This
phenomenon became known as animal electricity — a misnomer, as the
theory was later disproven. Prompted by these experiments, Volta initiated a
series of experiments using zinc, lead, tin or iron as positive plates. Copper,
silver, gold or graphite were used as negative plates.
Volta discovered in 1800 that a continuous flow of electrical force was
generated when using certain fluids as conductors to promote a chemical
reaction between the metals or electrodes. This led to the invention of the first
voltaic cell, better know as the battery. Volta discovered further that the
voltage would increase when voltaic cells were stacked on top of each other.
Figure 1-2: Four variations of Volta’s electric battery.
Silver and zinc disks are separated with moist paper. ©Cadex Electronics Inc.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 6 > Chapter 8 > Chapter 9 > Chapter 15 > Chapter 4 > Chapter 5
> Chapter 7 > Chapter 10 > Chapter 12 > Chapter 16 > Chapter 11 > Chapter 13 > Neue Artikel > Articulos Nuevos > Articles Nouveaux > Werden
Lithium-Ion Akkus sich im neuen Millennium behaupten? > ¿Las baterías de Litio-Ion energizaran el nuevo milenio? > Was begrenzt die Betriebszeit eines
Akkus? > El secreto del tiempo de duración en las baterías > Welcher Akku hält länger? > Akku-Geheimnis gelöst! > Table of Contents > Author's Note >
Introduction > Chapter 1
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In the same year, Volta released his discovery of a continuous source of
electricity to the Royal Society of London. No longer were experiments
limited to a brief display of sparks that lasted a fraction of a second. A
seemingly endless stream of electric current was now available.
France was one of the first nations to officially recognize Volta’s discoveries.
At the time, France was approaching the height of scientific advancements
and new ideas were welcomed with open arms to support the political agenda.
By invitation, Volta addressed the Institute of France in a series of lectures at
which Napoleon Bonaparte was present as a member of the Institute.
Figure 1-3: Volta’s experimentations at the French National Institute.
Volta’s discoveries so impressed the world that in November 1800, he was
invited by the French National Institute to lectures in which Napoleon
Bonaparte participated. Later, Napoleon himself helped with the experiments,
drawing sparks from the battery, melting a steel wire, discharging an electric
pistol and decomposing water into its elements. ©Cadex Electronics Inc.
New discoveries were made when Sir Humphry Davy, inventor of the miner’s
safety lamp, installed the largest and most powerful electric battery in the
vaults of the Royal Institution of London. He connected the battery to
charcoal electrodes and produced the first electric light. As reported by
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witnesses, his voltaic arc lamp produced “the most brilliant ascending arch of
light ever seen.”
Davy's most important investigations were devoted to electrochemistry.
Following Galvani's experiments and the discovery of the voltaic cell, interest
in galvanic electricity had become widespread. Davy began to test the
chemical effects of electricity in 1800. He soon found that by passing
electrical current through some substances, these substances decomposed, a
process later called electrolysis. The generated voltage was directly related to
the reactivity of the electrolyte with the metal. Evidently, Davy understood
that the actions of electrolysis and the voltaic cell were the same.
In 1802, Dr. William Cruickshank designed the first electric battery capable
of mass production. Cruickshank had arranged square sheets of copper, which
he soldered at their ends, together with sheets of zinc of equal size. These
sheets were placed into a long rectangular wooden box that was sealed with
cement. Grooves in the box held the metal plates in position. The box was
then filled with an electrolyte of brine, or watered down acid.
The third method of generating electricity was discovered relatively late —
electricity through magnetism. In 1820, André-Marie Ampère (1775-1836)
had noticed that wires carrying an electric current were at times attracted to
one another while at other times they were repelled.
In 1831, Michael Faraday (1791-1867) demonstrated how a copper disc was
able to provide a constant flow of electricity when revolved in a strong
magnetic field. Faraday, assisting Davy and his research team, succeeded in
generating an endless electrical force as long as the movement between a coil
and magnet continued. The electric generator was invented. This process was
then reversed and the electric motor was discovered. Shortly thereafter,
transformers were developed that could convert electricity to a desired
voltage. In 1833, Faraday established the foundation of electrochemistry with
Faraday's Law, which describes the amount of reduction that occurs in an
electrolytic cell.
In 1836, John F. Daniell, an English chemist, developed an improved battery
which produced a steadier current than Volta's device. Until then, all batteries
had been composed of primary cells, meaning that they could not be
recharged. In 1859, the French physician Gaston Platé invented the first
rechargeable battery. This secondary battery was based on lead acid
chemistry, a system that is still used today.
Figure 1-4: Cruickshank and the first flooded battery.
William Cruickshank, an English chemist, built a battery of electric cells by
joining zinc and copper plates in a wooden box filled with electrolyte. This
flooded design had the advantage of not drying out with use and provided
more energy than Volta’s disc arrangement. ©Cadex Electronics Inc.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 6 > Chapter 8 > Chapter 9 > Chapter 15 > Chapter 4 > Chapter 5
> Chapter 7 > Chapter 10 > Chapter 12 > Chapter 16 > Chapter 11 > Chapter 13 > Neue Artikel > Articulos Nuevos > Articles Nouveaux > Werden
Lithium-Ion Akkus sich im neuen Millennium behaupten? > ¿Las baterías de Litio-Ion energizaran el nuevo milenio? > Was begrenzt die Betriebszeit eines
Akkus? > El secreto del tiempo de duración en las baterías > Welcher Akku hält länger? > Akku-Geheimnis gelöst! > Table of Contents > Author's Note >
Introduction > Chapter 1
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Toward the end of the 1800s, giant generators and transformers were built.
Transmission lines were installed and electricity was made available to humanity
to produce light, heat and movement. In the early twentieth century, the use of
electricity was further refined. The invention of the vacuum tube enabled
generating controlled signals, amplifications and sound. Soon thereafter, radio was
invented, which made wireless communication possible.
In 1899, Waldmar Jungner from Sweden invented the nickel-cadmium
battery, which used nickel for the positive electrode and cadmium for the
negative. Two years later, Edison produced an alternative design by replacing
cadmium with iron. Due to high material costs compared to dry cells or lead
acid storage batteries, the practical applications of the nickel-cadmium and
nickel-iron batteries were limited.
It was not until Shlecht and Ackermann invented the sintered pole plate in
1932 that large improvements were achieved. These advancements were
reflected in higher load currents and improved longevity. The sealed
nickel-cadmium battery, as we know it toady, became only available when
Neumann succeeded in completely sealing the cell in 1947.
From the early days on, humanity became dependent on electricity, a product
without which our technological advancements would not have been possible.
With the increased need for mobility, people moved to portable power storage
— first for wheeled applications, then for portable and finally wearable use.
As awkward and unreliable as the early batteries may have been, our
descendants may one day look at today’s technology in a similar way to how
we view our predecessors’ clumsy experiments of 100 years ago.
History of Battery Development
1600
1791
1800
1802
Gilbert (England)
Galvani (Italy)
Volta (Italy)
Cruickshank (England)
1820
1833
1836
1859
1868
1888
1899
Ampère (France)
Faraday (England)
Daniell (England)
Planté (France)
Leclanché (France)
Gassner (USA)
Jungner (Sweden)
Establishment electrochemistry study
Discovery of ‘animal electricity’
Invention of the voltaic cell
First electric battery capable of mass
production
Electricity through magnetism
Announcement of Faraday’s Law
Invention of the Daniell cell
Invention of the lead acid battery
Invention of the Leclanché cell
Completion of the dry cell
Invention of the nickel-cadmium
battery
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1901
1932
Edison (USA)
Shlecht & Ackermann
(Germany)
Neumann (France)
1947
Mid 1960 Union Carbide (USA)
Mid 1970
1990
1992
1999
2001
Kordesch (Canada)
Invention of the nickel-iron battery
Invention of the sintered pole plate
Successfully sealing the
nickel-cadmium battery
Development of primary alkaline
battery
Development of valve regulated lead
acid battery
Commercialization nickel-metal
hydride battery
Commercialization reusable alkaline
battery
Commercialization lithium-ion
polymer
Anticipated volume production of
proton exchange membrane fuel cell
Figure 1-5: History of battery development.
The battery may be much older. It is believed that the Parthians who ruled
Baghdad (ca. 250 bc) used batteries to electroplate silver. The Egyptians are
said to have electroplated antimony onto copper over 4300 years ago.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2
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Chapter 2: Battery
Chemistries
Battery novices often argue that advanced battery systems are now available
that offer very high energy densities, deliver 1000 charge/discharge cycles
and are paper thin. These attributes are indeed achievable — unfortunately not
in the same battery pack. A given battery may be designed for small size and
long runtime, but this pack would have a limited cycle life. Another battery
may be built for durability, but it would be big and bulky. A third pack may
have high energy density and long durability, but would be too expensive for
the commercial consumer.
Battery manufacturers are well aware of customer needs and have responded
by offering battery packs that best suit the specific application. The mobile
phone industry is an example of this clever adaptation. For this market, the
emphasis is placed on small size and high energy density. Longevity comes in
second.
The mention of NiMH on a battery pack does not automatically guarantee
high energy density. A prismatic NiMH battery for a mobile phone, for
example, is made for slim geometry and may only have an energy density of
60Wh/kg. The cycle count for this battery would be limited to around 300. In
comparison, a cylindrical NiMH offers energy densities of 80Wh/kg and
higher. Still, the cycle count of this battery will be moderate to low. High
durability NiMH batteries, which are intended for industrial use and the
electric vehicle enduring 1000 discharges to 80 percent depth-of discharge,
are packaged in large cylindrical cells. The energy density on these cells is a
modest 70Wh/kg.
Similarly, Li-ion batteries for defense applications are being produced that far
exceed the energy density of the commercial equivalent. Unfortunately, these
super-high capacity Li-ion batteries are deemed unsafe in the hands of the
public. Neither would the general public be able to afford to buy them.
When energy densities and cycle life are mentioned, this book refers to a
middle-of-the-road commercial battery that offers a reasonable compromise in
size, energy density, cycle life and price. The book excludes miracle batteries
that only live in controlled environments.
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Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
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or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2
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Let's examine the advantages and limitations of today’s popular battery
systems. Batteries are scrutinized not only in terms of energy density but
service life, load characteristics, maintenance requirements, self-discharge
and operational costs. Since NiCd remains a standard against which other
batteries are compared, let’s evaluate alternative chemistries against this
classic battery type.
Nickel Cadmium (NiCd) — mature and well understood but relatively low in
energy density. The NiCd is used where long life, high discharge rate and
economical price are important. Main applications are two-way radios,
biomedical equipment, professional video cameras and power tools. The NiCd
contains toxic metals and is not environmentally friendly.
Nickel-Metal Hydride (NiMH) — has a higher energy density compared to
the NiCd at the expense of reduced cycle life. NiMH contains no toxic metals.
Applications include mobile phones and laptop computers.
Lead Acid — most economical for larger power applications where weight is
of little concern. The lead acid battery is the preferred choice for hospital
equipment, wheelchairs, emergency lighting and UPS systems.
Lithium Ion (Li-ion) — fastest growing battery system. Li-ion is used where
high-energy density and light weight is of prime importance. The Li-ion is
more expensive than other systems and must follow strict guidelines to assure
safety. Applications include notebook computers and cellular phones.
Lithium Ion Polymer (Li-ion polymer) — a potentially lower cost version of
the Li-ion. This chemistry is similar to the Li-ion in terms of energy density.
It enables very slim geometry and allows simplified packaging. Main
applications are mobile phones.
Reusable Alkaline — replaces disposable household batteries; suitable for
low-power applications. Its limited cycle life is compensated by low
self-discharge, making this battery ideal for portable entertainment devices
and flashlights.
Figure 2-1 compares the characteristics of the six most commonly used
rechargeable battery systems in terms of energy density, cycle life, exercise
requirements and cost. The figures are based on average ratings of
commercially available batteries at the time of publication. Exotic batteries
with above average ratings are not included.
NiMH
Lead
Acid
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NiCd
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Li-ion
Li-ion Reusable
polymer Alkaline
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Gravimetric
45-80
Energy Density
(Wh/kg)
60-120 30-50
Internal
100 to
Resistance
2001
(includes
6V pack
peripheral
circuits) in mW
200 to
3001
6V
pack
<1001
12V
pack
150 to
2501
7.2V
pack
200 to
3001
7.2V
pack
200 to
20001
6V pack
110-160 100-130 80 (initial)
Cycle Life (to
80% of initial
capacity)
15002
300 to
5002,3
200 to
3002
500 to
10003
300 to
500
503
(to 50%)
Fast Charge
Time
1h
typical
2-4h
8-16h
2-4h
2-4h
2-3h
Overcharge
Tolerance
moderate low
high
very low low
moderate
5%
10%5
~10%5
0.3%
1.25V6
1.25V6 2V
3.6V
3.6V
1.5V
20C
1C
5C
5C7
0.5C or 0.2C
lower
>2C
1C or
lower
>2C
1C or
lower
0.5C
0.2C or
lower
Operating
-40 to
Temperature 60°C
(discharge only)
-20 to
60°C
-20 to
60°C
0 to
60°C
0 to
65°C
Maintenance
Requirement
60 to
3 to 6 not req. not req. not req.
90 days months9
Self-discharge 20%4
/ Month (room
temperature)
Cell Voltage
(nominal)
Load Current
- peak
- best result
30 to
60 days
30%4
-20 to
60°C
Typical
$50
Battery Cost
(7.2V)
(US$, reference
only)
$60
(7.2V)
$25
(6V)
$100
(7.2V)
$100
(7.2V)
$5
(9V)
Cost per Cycle $0.04
(US$)11
$0.12
$0.10
$0.14
$0.29
$0.10-0.50
Commercial
use since
1990
1970
1991
1999
1992
1950
Figure 2-1:
Characteristics of commonly used rechargeable batteries.
The figures are based on average ratings of batteries available commercially
at the time of publication; experimental batteries with above average ratings
are not included.
1. Internal resistance of a battery pack varies with cell rating, type of
protection circuit and number of cells. Protection circuit of Li-ion and
Li-polymer adds about 100mW.
2. Cycle life is based on battery receiving regular maintenance. Failing to
apply periodic full discharge cycles may reduce the cycle life by a
factor of three.
3. Cycle life is based on the depth of discharge. Shallow discharges
provide more cycles than deep discharges.
4. The discharge is highest immediately after charge, then tapers off. The
5.
6.
7.
8.
9.
10.
11.
NiCd capacity decreases 10% in the first 24h, then declines to about
10% every 30 days thereafter. Self-discharge increases with higher
temperature.
Internal protection circuits typically consume 3% of the stored energy
per month.
1.25V is the open cell voltage. 1.2V is the commonly used value. There
is no difference between the cells; it is simply a method of rating.
Capable of high current pulses.
Applies to discharge only; charge temperature range is more confined.
Maintenance may be in the form of ‘equalizing’ or ‘topping’ charge.
Cost of battery for commercially available portable devices.
Derived from the battery price divided by cycle life. Does not include
the cost of electricity and chargers.
Observation: It is interesting to note that NiCd has the shortest charge time,
delivers the highest load current and offers the lowest overall cost-per-cycle,
but has the most demanding maintenance requirements.
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The Nickel Cadmium (NiCd) Battery
Alkaline nickel battery technology originated in 1899, when Waldmar
Jungner invented the NiCd battery. The materials were expensive compared to
other battery types available at the time and its use was limited to special
applications. In 1932, the active materials were deposited inside a porous
nickel-plated electrode and in 1947, research began on a sealed NiCd battery,
which recombined the internal gases generated during charge rather than
venting them. These advances led to the modern sealed NiCd battery, which is
in use today.
The NiCd prefers fast charge to slow charge and pulse charge to DC charge.
All other chemistries prefer a shallow discharge and moderate load currents.
The NiCd is a strong and silent worker; hard labor poses no problem. In fact,
the NiCd is the only battery type that performs best under rigorous working
conditions. It does not like to be pampered by sitting in chargers for days and
being used only occasionally for brief periods. A periodic full discharge is so
important that, if omitted, large crystals will form on the cell plates (also
referred to as 'memory') and the NiCd will gradually lose its performance.
Among rechargeable batteries, NiCd remains a popular choice for
applications such as two-way radios, emergency medical equipment,
professional video cameras and power tools. Over 50 percent of all
rechargeable batteries for portable equipment are NiCd. However, the
introduction of batteries with higher energy densities and less toxic metals is
causing a diversion from NiCd to newer technologies.
Advantages and Limitations of NiCd Batteries
Advantages Fast and simple charge — even after prolonged storage.
High number of charge/discharge cycles — if properly
maintained, the NiCd provides over 1000 charge/discharge
cycles.
Good load performance — the NiCd allows recharging at low
temperatures.
Long shelf life – in any state-of-charge.
Simple storage and transportation — most airfreight companies
accept the NiCd without special conditions.
Good low temperature performance.
Forgiving if abused — the NiCd is one of the most rugged
rechargeable batteries.
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Economically priced — the NiCd is the lowest cost battery in
terms of cost per cycle.
Available in a wide range of sizes and performance options —
most NiCd cells are cylindrical.
Limitations Relatively low energy density — compared with newer
systems.
Memory effect — the NiCd must periodically be exercised to
prevent memory.
Environmentally unfriendly — the NiCd contains toxic metals.
Some countries are limiting the use of the NiCd battery.
Has relatively high self-discharge — needs recharging after
storage.
Figure 2-2:
Advantages and limitations of NiCd batteries.
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The Nickel-Metal Hydride (NiMH)
Battery
Research of the NiMH system started in the 1970s as a means of discovering
how to store hydrogen for the nickel hydrogen battery. Today, nickel
hydrogen batteries are mainly used for satellite applications. They are bulky,
contain high-pressure steel canisters and cost thousands of dollars each.
In the early experimental days of the NiMH battery, the metal hydride alloys
were unstable in the cell environment and the desired performance
characteristics could not be achieved. As a result, the development of the
NiMH slowed down. New hydride alloys were developed in the 1980s that
were stable enough for use in a cell. Since the late 1980s, NiMH has steadily
improved, mainly in terms of energy density.
The success of the NiMH has been driven by its high energy density and the
use of environmentally friendly metals. The modern NiMH offers up to
40 percent higher energy density compared to NiCd. There is potential for yet
higher capacities, but not without some negative side effects.
Both NiMH and NiCd are affected by high self-discharge. The NiCd loses
about 10 percent of its capacity within the first 24 hours, after which the
self-discharge settles to about 10 percent per month. The self-discharge of the
NiMH is about one-and-a-half to two times greater compared to NiCd.
Selection of hydride materials that improve hydrogen bonding and reduce
corrosion of the alloy constituents reduces the rate of self-discharge, but at the
cost of lower energy density.
The NiMH has been replacing the NiCd in markets such as wireless
communications and mobile computing. In many parts of the world, the buyer
is encouraged to use NiMH rather than NiCd batteries. This is due to
environmental concerns about careless disposal of the spent battery.
The question is often asked, “Has NiMH improved over the last few years?”
Experts agree that considerable improvements have been achieved, but the
limitations remain. Most of the shortcomings are native to the nickel-based
technology and are shared with the NiCd battery. It is widely accepted that
NiMH is an interim step to lithium battery technology.
Initially more expensive than the NiCd, the price of the NiMH has dropped
and is now almost at par value. This was made possible with high volume
production. With a lower demand for NiCd, there will be a tendency for the
price to increase.
Advantages and Limitations of NiMH Batteries
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Advantages 30 – 40 percent higher capacity over a standard NiCd. The
NiMH has potential for yet higher energy densities.
Less prone to memory than the NiCd. Periodic exercise cycles
are required less often.
Simple storage and transportation — transportation conditions
are not subject to regulatory control.
Environmentally friendly — contains only mild toxins;
profitable for recycling.
Limitations Limited service life — if repeatedly deep cycled, especially at
high load currents, the performance starts to deteriorate after
200 to 300 cycles. Shallow rather than deep discharge cycles
are preferred.
Limited discharge current — although a NiMH battery is
capable of delivering high discharge currents, repeated
discharges with high load currents reduces the battery’s cycle
life. Best results are achieved with load currents of 0.2C to
0.5C (one-fifth to one-half of the rated capacity).
More complex charge algorithm needed — the NiMH
generates more heat during charge and requires a longer charge
time than the NiCd. The trickle charge is critical and must be
controlled carefully.
High self-discharge — the NiMH has about 50 percent higher
self-discharge compared to the NiCd. New chemical additives
improve the self-discharge but at the expense of lower energy
density.
Performance degrades if stored at elevated temperatures — the
NiMH should be stored in a cool place and at a state-of-charge
of about 40 percent.
High maintenance — battery requires regular full discharge to
prevent crystalline formation.
About 20 percent more expensive than NiCd — NiMH
batteries designed for high current draw are more expensive
than the regular version.
Figure 2-3:
Advantages and limitations of NiMH batteries
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The Lead Acid Battery
Invented by the French physician Gaston Planté in 1859, lead acid was the
first rechargeable battery for commercial use. Today, the flooded lead acid
battery is used in automobiles, forklifts and large uninterruptible power
supply (UPS) systems.
During the mid 1970s, researchers developed a maintenance-free lead acid
battery, which could operate in any position. The liquid electrolyte was
transformed into moistened separators and the enclosure was sealed. Safety
valves were added to allow venting of gas during charge and discharge.
Driven by diverse applications, two
designations of batteries emerged.
They are the sealed lead acid (SLA),
also known under the brand name of
Gelcell, and the valve regulated lead
acid (VRLA). Technically, both
batteries are the same. No scientific
definition exists as to when an SLA
becomes a VRLA. (Engineers may
argue that the word ‘sealed lead acid’ is a misnomer because no lead acid
battery can be totally sealed. In essence, all are valve regulated.)
The SLA has a typical capacity range of 0.2Ah to 30Ah and powers portable
and wheeled applications. Typical uses are personal UPS units for PC backup,
small emergency lighting units, ventilators for health care patients and
wheelchairs. Because of low cost, dependable service and minimal
maintenance requirements, the SLA battery is the preferred choice for
biomedical and health care instruments in hospitals and retirement homes.
The VRLA battery is generally used for stationary applications. Their
capacities range from 30Ah to several thousand Ah and are found in larger
UPS systems for power backup. Typical uses are mobile phone repeaters,
cable distribution centers, Internet hubs and utilities, as well as power backup
for banks, hospitals, airports and military installations.
Unlike the flooded lead acid battery, both the SLA and VRLA are designed
with a low over-voltage potential to prohibit the battery from reaching its
gas-generating potential during charge. Excess charging would cause gassing
and water depletion. Consequently, the SLA and VRLA can never be charged
to their full potential.
Among modern rechargeable batteries, the lead acid battery family has the
lowest energy density. For the purpose of analysis, we use the term ‘sealed
lead acid’ to describe the lead acid batteries for portable use and ‘valve
regulated lead acid’ for stationary applications. Because of our focus on
portable batteries, we focus mainly on the SLA.
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The SLA is not subject to memory.
Leaving the battery on float charge for a
prolonged time does not cause damage.
The battery’s charge retention is best
among rechargeable batteries. Whereas the
NiCd self-discharges approximately
40 percent of its stored energy in three
months, the SLA self-discharges the same
amount in one year. The SLA is relatively inexpensive to purchase but the
operational costs can be more expensive than the NiCd if full cycles are
required on a repetitive basis.
The SLA does not lend itself to fast charging — typical charge times are
8 to 16 hours. The SLA must always be stored in a charged state. Leaving the
battery in a discharged condition causes sulfation, a condition that makes the
battery difficult, if not impossible, to recharge.
Unlike the NiCd, the SLA does not like deep cycling. A full discharge causes
extra strain and each discharge/charge cycle robs the battery of a small
amount of capacity. This loss is very small while the battery is in good
operating condition, but becomes more acute once the performance drops
below 80 percent of its nominal capacity. This wear-down characteristic also
applies to other battery chemistries in varying degrees. To prevent the battery
from being stressed through repetitive deep discharge, a larger SLA battery is
recommended.
Depending on the depth of discharge and operating temperature, the SLA
provides 200 to 300 discharge/charge cycles. The primary reason for its
relatively short cycle life is grid corrosion of the positive electrode, depletion
of the active material and expansion of the positive plates. These changes are
most prevalent at higher operating temperatures. Applying charge/discharge
cycles does not prevent or reverse the trend.
There are some methods that improve the performance and prolong the life of
the SLA. The optimum operating temperature for a VRLA battery is 25°C
(77°F). As a rule of thumb, every 8°C (15°F) rise in temperature will cut the
battery life in half. VRLA that would last for 10 years at 25°C would only be
good for 5 years if operated at 33°C (95°F). The same battery would endure a
little more than one year at a temperature of 42°C (107°F).
Advantages and Limitations of Lead Acid Batteries
Advantages Inexpensive and simple to manufacture — in terms of cost per
watt hours, the SLA is the least expensive.
Mature, reliable and well-understood technology — when used
correctly, the SLA is durable and provides dependable service.
Low self-discharge —the self-discharge rate is among the
lowest in rechargeable batterysystems.
Low maintenance requirements — no memory; no electrolyte
to fill.
Capable of high discharge rates.
Limitations Cannot be stored in a discharged condition.
Low energy density — poor weight-to-energy density limits
use to stationary and wheeled applications.
Allows only a limited number of full discharge cycles — well
suited for standby applications that require only occasional
deep discharges.
Environmentally unfriendly — the electrolyte and the lead
content can cause environmental damage.
Transportation restrictions on flooded lead acid — there are
environmental concerns regarding spillage in case of an
accident.
Thermal runaway can occur with improper charging.
Figure 2-4:
Advantages and limitations of lead acid batteries.
The SLA has a relatively low energy density compared with other
rechargeable batteries, making it unsuitable for handheld devices that demand
compact size. In addition, performance at low temperatures is greatly reduced.
The SLA is rated at a 5-hour discharge or 0.2C. Some batteries are even rated
at a slow 20 hour discharge. Longer discharge times produce higher capacity
readings. The SLA performs well on high pulse currents. During these pulses,
discharge rates well in excess of 1C can be drawn.
In terms of disposal, the SLA is less harmful than the NiCd battery but the
high lead content makes the SLA environmentally unfriendly. Ninety percent
of lead acid-based batteries are being recycled.
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Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article:
Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article:
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The Lithium Ion Battery
Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was
not until the early 1970s that the first non-rechargeable lithium batteries became
commercially available. Attempts to develop rechargeable lithium batteries
followed in the 1980s, but failed due to safety problems.
Lithium is the lightest of all metals, has the greatest electrochemical potential and
provides the largest energy density per weight. Rechargeable batteries using
lithium metal anodes (negative electrodes) are capable of providing both high
voltage and excellent capacity, resulting in an extraordinary high energy density.
After much research on rechargeable lithium batteries during the 1980s, it was
found that cycling causes changes on the lithium electrode. These
transformations, which are part of normal wear and tear, reduce the thermal
stability, causing potential thermal runaway conditions. When this occurs, the cell
temperature quickly approaches the melting point of lithium, resulting in a violent
reaction called ‘venting with flame’. A large quantity of rechargeable lithium
batteries sent to Japan had to be recalled in 1991 after a battery in a mobile phone
released flaming gases and inflicted burns to a person’s face.
Because of the inherent instability of lithium metal, especially during charging,
research shifted to a non-metallic lithium battery using lithium ions. Although
slightly lower in energy density than lithium metal, the Li-ion is safe, provided
certain precautions are met when charging and discharging. In 1991, the Sony
Corporation commercialized the first Li-ion battery. Other manufacturers
followed suit. Today, the Li-ion is the fastest growing and most promising battery
chemistry.
The energy density of the Li-ion is typically twice that of the standard NiCd.
Improvements in electrode active materials have the potential of increasing the
energy density close to three times that of the NiCd. In addition to high capacity,
the load characteristics are reasonably good and behave similarly to the NiCd in
terms of discharge characteristics (similar shape of discharge profile, but different
voltage). The flat discharge curve offers effective utilization of the stored power
in a desirable voltage spectrum.
The Li-ion is a low maintenance battery, an advantage that most other chemistries
cannot claim. There is no memory and no scheduled cycling is required to
prolong the battery’s life. In addition, the self-discharge is less than half
compared to NiCd and NiMH, making the Li-ion well suited for modern fuel
gauge applications.
The high cell voltage of Li-ion allows the manufacture of battery packs consisting
of only one cell. Many of today’s mobile phones run on a single cell, an
advantage that simplifies battery design. Supply voltages of electronic
applications have been heading lower, which in turn requires fewer cells per
battery pack. To maintain the same power, however, higher currents are needed.
This emphasizes the importance of very low cell resistance to allow unrestricted
flow of current.
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Chemistry variations — During recent years, several types of Li-ion batteries
have emerged with only one thing in common — the catchword 'lithium'.
Although strikingly similar on the outside, lithium-based batteries can vary
widely. This book addresses the lithium-based batteries that are predominantly
used in commercial products.
Sony’s original version of the Li-ion used coke, a product of coal, as the negative
electrode. Since 1997, most Li-ions (including Sony’s) have shifted to graphite.
This electrode provides a flatter discharge voltage curve than coke and offers a
sharp knee bend at the end of discharge (see Figure 2-5). As a result, the graphite
system delivers the stored energy by only having to discharge to 3.0V/cell,
whereas the coke version must be discharged to 2.5V to get similar runtime. In
addition, the graphite version is capable of delivering a higher discharge current
and remains cooler during charge and discharge than the coke version.
For the positive electrode, two distinct chemistries have emerged. They are cobalt
and spinel (also known as manganese). Whereas cobalt has been in use longer,
spinel is inherently safer and more forgiving if abused. Small prismatic spinel
packs for mobile phones may only include a thermal fuse and temperature sensor.
In addition to cost savings on a simplified protection circuit, the raw material cost
for spinel is lower than that of cobalt.
Figure 2-5:
Li-ion discharge characteristics.
The graphite Li-ion only needs to discharge to 3.0V/cell, whereas the coke
version must be discharged to 2.5V/cell to achieve similar performance.
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As a trade-off, spinel offers a slightly lower energy density, suffers capacity
loss at temperatures above 40°C and ages quicker than cobalt. Figure 2-6
compares the advantages and disadvantages of the two chemistries.
Cobalt
Manganese (Spinel)
Energy
density
(Wh/kg)
140 1
120 1
Safety
On overcharge, the cobalt
electrode provides extra
lithium, which can form
into metallic lithium,
causing a potential safety
risk if not protected by a
safety circuit.
On overcharge, the manganese
electrode runs out of lithium
causing the cell only to get
warm. Safety circuits can be
eliminated for small 1 and 2
cell packs.
Temperature Wide temperature range.
Best suited for operation at
elevated temperature.
Capacity loss above +40°C.
Not as durable at higher
temperatures.
Aging
Short-term storage possible.
Impedance increases with
age. Newer versions offer
longer storage.
Slightly less than cobalt.
Impedance changes little over
the life of the cell. Due to
continuous improvements,
storage time is difficult to
predict.
Life
Expectancy
300 cycles, 50% capacity at May be shorter than cobalt.
500 cycles.
Cost
Raw material relatively
Raw material 30% lower than
high; protection circuit adds cobalt. Cost advantage on
to costs.
simplified protection circuit.
Figure 2-6:
Comparison of cobalt and manganese as positive electrodes.
Manganese is inherently safer and more forgiving if abused but offers a
slightly lower energy density. Manganese suffers capacity loss at temperature
above 40°C and ages quicker than cobalt.
Based on present generation 18650 cells. The energy density tends to be lower
for prismatic cells.
The choice of metals, chemicals and additives help balance the critical
trade-off between high energy density, long storage time, extended cycle life
and safety. High energy densities can be achieved with relative ease. For
example, adding more nickel in lieu of cobalt increases the ampere/hours
rating and lowers the manufacturing cost but makes the cell less safe. While a
start-up company may focus on high energy density to gain quick market
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acceptance, safety, cycle life and storage capabilities may be compromised.
Reputable manufacturers, such as Sony, Panasonic, Sanyo, Moli Energy and
Polystor place high importance on safety. Regulatory authorities assure that
only safe batteries are sold to the public.
Li-ion cells cause less harm when disposed of than lead or cadmium-based
batteries. Among the Li-ion family, the spinel is the friendliest in terms of
disposal.
Despite its overall advantages, Li-ion also has its drawbacks. It is fragile and
requires a protection circuit to maintain safe operation. Built into each pack,
the protection circuit limits the peak voltage of each cell during charge and
prevents the cell voltage from dropping too low on discharge. In addition, the
maximum charge and discharge current is limited and the cell temperature is
monitored to prevent temperature extremes. With these precautions in place,
the possibility of metallic lithium plating occurring due to overcharge is
virtually eliminated.
Aging is a concern with most Li-ion batteries. For unknown reasons, battery
manufacturers are silent about this issue. Some capacity deterioration is
noticeable after one year, whether the battery is in use or not. Over two or
perhaps three years, the battery frequently fails. It should be mentioned that
other chemistries also have age-related degenerative effects. This is especially
true for the NiMH if exposed to high ambient temperatures.
Storing the battery in a cool place slows down the aging process of the Li-ion
(and other chemistries). Manufacturers recommend storage temperatures of
15°C (59°F). In addition, the battery should only be partially charged when in
storage.
Extended storage is not recommended for Li-ion batteries. Instead, packs
should be rotated. The buyer should be aware of the manufacturing date when
purchasing a replacement Li-ion battery. Unfortunately, this information is
often encoded in an encrypted serial number and is only available to the
manufacturer.
Manufacturers are constantly improving the chemistry of the Li-ion battery.
Every six months, a new and enhanced chemical combination is tried. With
such rapid progress, it becomes difficult to assess how well the revised battery
ages and how it performs after long-term storage.
Cost analysis — The most economical lithium-based battery in terms of
cost-to-energy ratio is a pack using the cylindrical 18650 cell. This battery is
somewhat bulky but suitable for portable applications such as mobile
computing. If a slimmer pack is required (thinner than 18 mm), the prismatic
Li-ion cell is the best choice. There is little or no gain in energy density per
weight and size over the 18650, however the cost is more than double.
If an ultra-slim geometry is needed (less than 4 mm), the best choice is Li-ion
polymer. This is the most expensive option in terms of energy cost. The
Li-ion polymer does not offer appreciable energy gains over conventional
Li-ion systems, nor does it match the durability of the 18560 cell.
Advantages and Limitations of Li-ion Batteries
Advantages High energy density — potential for yet higher capacities.
Relatively low self-discharge — self-discharge is less than half
that of NiCd and NiMH.
Low Maintenance — no periodic discharge is needed; no
memory.
Limitations Requires protection circuit — protection circuit limits voltage
and current. Battery is safe if not provoked.
Subject to aging, even if not in use — storing the battery in a
cool place and at 40 percent state-of-charge reduces the aging
effect.
Moderate discharge current.
Subject to transportation regulations — shipment of larger
quantities of Li-ion batteries may be subject to regulatory
control. This restriction does not apply to personal carry-on
batteries.
Expensive to manufacture — about 40 percent higher in cost
than NiCd. Better manufacturing techniques and replacement
of rare metals with lower cost alternatives will likely reduce the
price.
Not fully mature — changes in metal and chemical
combinations affect battery test results, especially with some
quick test methods.
Figure 2-7:
Advantages and limitations of Li-ion batteries.
Caution: Li-ion batteries have a high energy density. Exercise precaution
when handling and testing. Do not short circuit, overcharge, crush, drop,
mutilate, penetrate, apply reverse polarity, expose to high temperature or
disassemble. Only use the Li-ion battery with the designated protection
circuit. High case temperature resulting from abuse of the cell could cause
physical injury. The electrolyte is highly flammable. Rupture may cause
venting with flame.
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The Lithium Polymer Battery
The Li-polymer differentiates itself from other battery systems in the type of
electrolyte used. The original design, dating back to the 1970s, uses a dry
solid polymer electrolyte only. This electrolyte resembles a plastic-like film
that does not conduct electricity but allows an exchange of ions (electrically
charged atoms or groups of atoms). The polymer electrolyte replaces the
traditional porous separator, which is soaked with electrolyte.
The dry polymer design offers simplifications with respect to fabrication,
ruggedness, safety and thin-profile geometry. There is no danger of
flammability because no liquid or gelled electrolyte is used.
With a cell thickness measuring as little as one millimeter (0.039 inches),
equipment designers are left to their own imagination in terms of form, shape
and size. It is possible to create designs which form part of a protective
housing, are in the shape of a mat that can be rolled up, or are even embedded
into a carrying case or piece of clothing. Such innovative batteries are still a
few years away, especially for the commercial market.
Unfortunately, the dry Li-polymer suffers from poor conductivity. Internal
resistance is too high and cannot deliver the current bursts needed for modern
communication devices and spinning up the hard drives of mobile computing
equipment. Although heating the cell to 60°C (140°F) and higher increases
the conductivity to acceptable levels, this requirement is unsuitable in
commercial applications.
Research is continuing to develop a dry solid Li-polymer battery that
performs at room temperature. A dry solid Li-polymer version is expected to
be commercially available by 2005. It is expected to be very stable; would run
1000 full cycles and would have higher energy densities than today’s Li-ion
battery.
In the meantime, some Li-polymers are used as standby batteries in hot
climates. One manufacturer has added heating elements that keeps the battery
in the conductive temperature range at all times. Such a battery performs well
for the application intended because high ambient temperatures do not affect
the service life of this battery in the same way it does the VRLA, for example.
To make a small Li-polymer battery conductive, some gelled electrolyte has
been added. Most of the commercial Li-polymer batteries used today for
mobile phones are a hybrid and contain gelled electrolyte. The correct term
for this system is ‘Lithium Ion Polymer’. For promotional reasons, most
battery manufacturers mark the battery simply as Li-polymer. Since the
hybrid lithium polymer is the only functioning polymer battery for portable
use today, we will focus on this chemistry.
With gelled electrolyte added, what then is the difference between Li-ion and
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Li-ion polymer? Although the characteristics and performance of the two
systems are very similar, the Li-ion polymer is unique in that it uses a solid
electrolyte, replacing the porous separator. The gelled electrolyte is simply
added to enhance ion conductivity.
Technical difficulties and delays in volume manufacturing have deferred the
introduction of the Li-ion polymer battery. This postponement, as some critics
argue, is due to ‘cashing in’ on the Li-ion battery. Manufacturers have
invested heavily in research, development and equipment to mass-produce the
Li-ion. Now businesses and shareholders want to see a return on their
investment.
In addition, the promised superiority of the Li-ion polymer has not yet been
realized. No improvements in capacity gains have been achieved — in fact,
the capacity is slightly less than that of the standard Li-ion battery. For the
present, there is no cost advantage in using the Li-ion polymer battery. The
thin profile has, however, compelled mobile phone manufacturers to use this
promising technology for their new generation handsets.
One of the advantages of the Li-ion polymer, however, is simpler packaging
because the electrodes can easily be stacked. Foil packaging, similar to that
used in the food industry, is being used. No defined norm in cell size has been
established by the industry.
Advantages and Limitations of Li-ion Polymer Batteries
Advantages Very low profile — batteries that resemble the profile of a
credit card are feasible.
Flexible form factor — manufacturers are not bound by
standard cell formats. With high volume, any reasonable size
can be produced economically.
Light weight – gelled rather than liquid electrolytes enable
simplified packaging, in some cases eliminating the metal shell.
Improved safety — more resistant to overcharge; less chance
for electrolyte leakage.
Limitations Lower energy density and decreased cycle count compared to
Li-ion — potential for improvements exist.
Expensive to manufacture — once mass-produced, the Li-ion
polymer has the potential for lower cost. Reduced control
circuit offsets higher manufacturing costs.
Figure 2-8:
Advantages and limitations of Li-ion polymer batteries.
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Reusable Alkaline Batteries
The idea of recharging alkaline batteries is not new. Although not endorsed by
manufacturers, ordinary alkaline batteries have been recharged in households
for many years. Recharging these batteries is only effective, however, if the
cells have been discharged to less than 50 percent of their total capacity. The
number of recharges depends solely on the depth of discharge and is limited
to a few at best. With each recharge, less capacity can be reclaimed. There is a
cautionary advisory, however: charging ordinary alkaline batteries may
generate hydrogen gas, which can lead to explosion. It is therefore not prudent
to charge ordinary alkaline unsupervised.
In comparison, the reusable alkaline is designed for repeated recharge. It too
loses charge acceptance with each recharge. The longevity of the reusable
alkaline is a direct function of the depth of discharge; the deeper the
discharge, the fewer cycles the battery can endure.
Tests performed by Cadex on ‘AA’ reusable alkaline cells showed a very high
capacity reading on the first discharge. In fact, the energy density was similar
to that of a NiMH battery. When the battery was discharged, then later
recharged using the manufacturer’s charger, the reusable alkaline settled at
60 percent, a capacity slightly below that of a NiCd. Repeat cycling in the
same manner resulted in a fractional capacity loss with each cycle. In our
tests, the discharge current was adjusted to 200mA (0.2 C-rate, or one fifth of
the rated capacity); the end-of-discharge threshold was set to 1V/cell.
An additional limitation of the reusable alkaline system is its low load current
capability of 400mA (lower than 400mA provides better results). Although
adequate for portable AM/FM radios, CD players, tape players and
flashlights, 400mA is insufficient to power most mobile phones and video
cameras.
The reusable alkaline is inexpensive but the cost per cycle is high when
compared to the nickel-based rechargeables. Whereas the NiCd checks in at
$0.04 per cycle based on 1500 cycles, the reusable alkaline costs $0.50 based
on 10 full discharge cycles. For many applications, this seemingly high cost is
still economical when compared to the non-reusable alkaline that has a
one-time use. If the reusable alkaline battery is only partially discharged
before recharge, an improved cycle life is possible. At 50 percent depth of
discharge, 50 cycles can be expected.
To compare the operating cost between the standard and reusable alkaline, a
study was done on flashlight batteries for hospital use. The low-intensity care
unit using the flashlights only occasionally achieved measurable savings by
employing the reusable alkaline. The high-intensity unit that used the
flashlights constantly, on the other hand, did not attain the same result. Deeper
discharge and more frequent recharge reduced their service life and offset any
cost advantage over the standard alkaline battery.
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In summary, the standard alkaline offers maximum energy density whereas
the reusable alkaline provides the benefit of allowing some recharging. The
compromise of the reusable alkaline is loss of charge acceptance after the first
recharge.
Advantages and Limitations of Reusable Alkaline Batteries
Advantages Inexpensive and readily available — can be used as a direct
replacement of non-rechargeable (primary) cells.
More economical than non-rechargeable – allows several
recharges.
Low self-discharge — can be stored as a standby battery for up
to 10 years.
Environmentally friendly — no toxic metals used, fewer
batteries are discarded, reduces landfill.
Maintenance free — no need for cycling; no memory.
Limitations Limited current handling — suited for light-duty applications
like portable home entertainment, flashlights.
Limited cycle life — for best results, recharge before the
battery gets too low.
Figure 2-9:
Advantages and limitations of reusable alkaline batteries.
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The Supercapacitor
The supercapacitor resembles a regular capacitor with the exception that it
offers very high capacitance in a small size. Energy storage is by means of
static charge. Applying a voltage differential on the positive and negative
plates charges the supercapacitor. This concept is similar to an electrical
charge that builds up when walking on a carpet. Touching an object at ground
potential releases the energy. The supercapacitor concept has been around for
a number of years and has found many niche applications.
Whereas a regular capacitor consists of conductive foils and a dry separator,
the supercapacitor is a cross between a capacitor and an electro-chemical
battery. It uses special electrodes and some electrolyte. There are three kinds
of electrode materials suitable for the supercapacitor, namely: high surface
area activated carbons, metal oxide and conducting polymers. The one using
high surface area activated carbons is the most economical to manufacture.
This system is also called Double Layer Capacitor (DLC) because the energy
is stored in the double layer formed near the carbon electrode surface.
The electrolyte may be aqueous or organic. The aqueous electrolyte offers
low internal resistance but limits the voltage to one volt. In contrast, the
organic electrolyte allows two and three volts of charge, but the internal
resistance is higher.
To make the supercapacitor practical for use in electronic circuits, higher
voltages are needed. Connecting the cells in series accomplishes this task. If
more than three or four capacitors are connected in series, voltage balancing
must be used to prevent any cell from reaching over-voltage.
The amount of energy a capacitor can hold is measured in microfarads or µF.
(1µF = 0.000,001 farad). Small capacitors are measured in nanofarads (1000
times smaller than 1µF) and picofarads (1 million times smaller than 1µF).
Supercapacitors are rated in units of 1 farad and higher. The gravimetric
energy density is 1 to 10Wh/kg. This energy density is high in comparison to
the electrolytic capacitor but lower than batteries. A relatively low internal
resistance offers good conductivity.
The supercapacitor provides the energy of approximately one tenth that of the
NiMH battery. Whereas the electro-chemical battery delivers a fairly steady
voltage in the usable energy spectrum, the voltage of the supercapacitor is
linear and drops from full voltage to zero volts without the customary flat
voltage curve characterized by most chemical batteries. Because of this linear
discharge, the supercapacitor is unable to deliver the full charge. The
percentage of charge that is available depends on the voltage requirements of
the application.
If, for example, a 6V battery is allowed to discharge to 4.5V before the
equipment cuts off, the supercapacitor reaches that threshold within the first
quarter of the discharge time. The remaining energy slips into an unusable
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voltage range. A DC-to-DC converter can be used to increase the voltage
range but this option adds costs and introduces inefficiencies of 10 to 15
percent.
The most common supercapacitor applications are memory backup and
standby power. In some special applications, the supercapacitor can be used
as a direct replacement of the electrochemical battery. Additional uses are
filtering and smoothing of pulsed load currents.
A supercapacitor can, for example, improve the current handling of a battery.
During low load current, the battery charges the supercapacitor. The stored
energy then kicks in when a high load current is requested. This enhances the
battery's performance, prolongs the runtime and even extends the longevity of
the battery. The supercapacitor will find a ready market for portable fuel cells
to compensate for the sluggish performance of some systems and enhance
peak performance.
If used as a battery enhancer, the supercapacitor can be placed inside the
portable equipment or across the positive and negative terminals in the battery
pack. If put into the equipment, provision must be made to limit the high
influx of current when the equipment is turned on.
Low impedance supercapacitors can be charged in seconds. The charge
characteristics are similar to those of an electro-chemical battery. The initial
charge is fairly rapid; the topping charge takes some extra time. In terms of
charging method, the supercapacitor resembles the lead acid cell. Full charge
takes place when a set voltage limit is reached. Unlike the electro-chemical
battery, the supercapacitor does not require a full-charge detection circuit.
Supercapacitors can also be trickle charged.
Limitations Unable to use the full energy spectrum - depending on the
application, not all energy is available. Low energy density - typically holds
one-fifth to one-tenth the energy of an electrochemical battery. Cells have low
voltages - serial connections are needed to obtain higher voltages. Voltage
balancing is required if more than three capacitors are connected in series.
High self-discharge - the self-discharge is considerably higher than that of an
electrochemical battery.
Advantages and Limitations of Supercapacitors
Advantages Virtually unlimited cycle life - not subject to the wear and
aging experienced by the electrochemical battery.
Low impedance - enhances pulse current handling by
paralleling with an electrochemical battery.
Rapid charging - low-impedance supercapacitors charge in
seconds.
Simple charge methods - voltage-limiting circuit compensates
for self-discharge; no full-charge detection circuit needed.
Cost-effective energy storage - lower energy density is
compensated by a very high cycle count.
Limitations Unable to use the full energy spectrum - depending on the
application, not all energy is available.
Low energy density - typically holds one-fifth to one-tenth the
energy of an electrochemical battery.
Cells have low voltages - serial connections are needed to
obtain higher voltages.
Voltage balancing is required if more than three capacitors are
connected in series.
High self-discharge - the self-discharge is considerably higher
than that of an electrochemical battery.
Figure 2-10: Advantages and limitations of supercapacitors.
By nature, the voltage limiting circuit compensates for the self-discharge. The
supercapacitor can be recharged and discharged virtually an unlimited number
of times. Unlike the electrochemical battery, there is very little wear and tear
induced by cycling.
The self-discharge of the supercapacitor is substantially higher than that of the
electro-chemical battery. Typically, the voltage of the supercapacitor with an
organic electrolyte drops from full charge to the 30 percent level in as little as
10 hours.
Other supercapacitors can retain the charged energy longer. With these
designs, the capacity drops from full charge to 85 percent in 10 days. In 30
days, the voltage drops to roughly 65 percent and to 40 percent after 60 days.
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Chapter 3: The Battery Pack
In the 1700 and 1800s, cells were encased in glass jars. Later, larger batteries
were developed that used wooden containers. The inside was treated with a
sealant to prevent electrolyte leakage. With the need for portability, the
cylindrical cell appeared. After World War II, these cells became the standard
format for smaller, rechargeable batteries.
Downsizing required smaller and more compact cell design. The button cell,
which gained popularity in the 1980s, was a first attempt to achieve a
reasonably flat geometry, or obtain higher voltages in a compact profile by
stacking. The early 1990s brought the prismatic cell, which was followed by
the modern pouch cell.
This chapter addresses the cell designs, pack configurations and intrinsic
safety devices. In keeping with portability, this book addresses only the
smaller cells used for portable batteries.
The Cylindrical Cell
The cylindrical cell continues to be the most widely used packaging style. The
advantages are ease of manufacture and good mechanical stability. The
cylinder has the ability to withstand high internal pressures. While charging,
the cell pressure of a NiCd can reach 1379 kilopascals (kPa) or 200 pounds
per square inch (psi). A venting system is added on one end of the cylinder.
Venting occurs if the cell pressure reaches between 150 and 200 psi.
Figure 3-1 illustrates the conventional cell of a NiCd battery.
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Figure 3-1:
Cross-section of a classic NiCd cell.
The negative and positive plates are rolled together in a metal cylinder. The
positive plate is sintered and filled with nickel hydroxide. The negative plate
is coated with cadmium active material. A separator moistened with
electrolyte isolates the two plates. Design courtesy of Panasonic OEM Battery
Sales Group, March 2001.
The cylindrical cell is moderately priced and offers high energy density.
Typical applications are wireless communication, mobile computing,
biomedical instruments, power tools and other uses that do not demand
ultra-small size.
NiCd offers the largest selection of cylindrical cells. A good variety is also
available in the NiMH family, especially in the smaller cell formats. In
addition to cylindrical formats, NiMH also comes in the prismatic cell
packaging.
The Li-ion batteries are only available in limited cells sizes, the most popular
being the 18650. ‘Eighteen’ denotes the diameter in millimeters and ‘650’
describes the length in millimeters. The 18650 cell has a capacity of 1800 to
2000mAh. The larger 26650 cell has a diameter of 26 mm and delivers
3200mAh. Because of the flat geometry of the Li-ion polymer, this battery
chemistry is not available in a cylindrical format.
Most SLA batteries are built in a prismatic format, thus creating a rectangle
box that is commonly made of plastic materials. There are SLA batteries,
however, that take advantage of the cylindrical design by using a winding
technique that is similar to the conventional cell. The cylindrical Hawker
Cyclone SLA is said to offer improved cell stability, provide higher discharge
currents and have better temperature stability than the conventional prismatic
design.
The drawback of the cylindrical cell is less than maximum use of space.
When stacking the cells, air cavities are formed. Because of fixed cell size,
the pack must be designed around the available cell size.
Almost all cylindrical cells are equipped with a venting mechanism to expel
excess gases in an orderly manner. Whereas nickel-based batteries feature a
resealable vent, many cylindrical Li-ion contain a membrane seal that ruptures
if the pressure exceeds 3448 kPa (500 psi). There is usually some serious
swelling of the cell before the seal breaks. Venting only occurs under extreme
conditions.
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The Button Cell
The button cell was developed to miniaturize battery packs and solve stacking
problems. Today, this architecture is limited to a small niche market.
Non-rechargeable versions of the button cell continue to be popular and can
be found in watches, hearing aids and memory backup.
The main applications of the rechargeable button cell are (or were) older
cordless telephones, biomedical devices and industrial instruments. Although
small in design and inexpensive to manufacture, the main drawback is
swelling if charged too rapidly. Button cells have no safety vent and can only
be charged at a 10 to 16 hour charge rate. New designs claim rapid charge
capability.
Figure 3-2:
The button cell.
The button cell offers small size and ease of stacking but does not allow fast
charging. Coin cells, which are similar in appearance, are normally
lithium-based and are non-rechargeable. Photograph courtesy of Sanyo
Corporation; design courtesy of Panasonic OEM Battery Sales Group, March
2001.
The Prismatic Cell
The prismatic cell was developed in response to consumer demand for thinner
pack sizes. Introduced in the early 1990’s, the prismatic cell makes almost
maximum use of space when stacking. Narrow and elegant battery styles are
possible that suit today’s slim-style geometry. Prismatic cells are used
predominantly for mobile phone applications. Figure 3-3 shows the
prismatic cell.
Prismatic cells are most common in the lithium battery family. The Li-ion
polymer is exclusively prismatic. No universally accepted cell size exists for
Li-ion polymer batteries. One leading manufacturer may bring out one or
more sizes that fit a certain portable device, such as a mobile phone. While
these cells are produced at high volume, other cell manufacturers follow suit
and offer an identical cell at a competitive price. Prismatic cells that have
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gained acceptance are the 340648 and the 340848. Measured in millimeters,
‘34’ denotes the width, ‘06’ or ‘08’ the thickness and ‘48’ the length of
the cell.
Figure 3-3:
Cross-section of a prismatic cell.
The prismatic cell improves space utilization and allows more flexibility in
pack design. This cell construction is less cost effective than the cylindrical
equivalent and provides a slightly lower energy density. Design courtesy of
Polystor Corporation, March 2001.
Some prismatic cells are similar in size but are off by just a small fraction.
Such is the case with the Panasonic cell that measures 34 mm by 50 mm and
is 6.5 mm thick. If a few cubic millimeters can be added for a given
application, the manufacturer will do so for the sake of higher capacities.
The disadvantage of the prismatic cell is slightly lower energy densities
compared to the cylindrical equivalent. In addition, the prismatic cell is more
expensive to manufacture and does not provide the same mechanical stability
enjoyed by the cylindrical cell. To prevent bulging when pressure builds up,
heavier gauge metal is used for the container. The manufacturer allows some
degree of bulging when designing the battery pack.
The prismatic cell is offered in limited sizes and chemistries and runs from
about 400mAh to 2000mAh and higher. Because of the very large quantities
required for mobile phones, special prismatic cells are built to fit certain
models. Most prismatic cells do not have a venting system. In case of pressure
build-up, the cell starts to bulge. When correctly used and properly charged,
no swelling should occur.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
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The Pouch Cell
Cell design made a profound advance in 1995 when the pouch cell concept
was developed. Rather than using an expensive metallic cylinder and
glass-to-metal electrical feed-through to insulate the opposite polarity, the
positive and negative plates are enclosed in flexible, heat-sealable foils. The
electrical contacts consist of conductive foil tabs that are welded to the
electrode and sealed to the pouch material. Figure 3-4 illustrates the
pouch cell.
The pouch cell concept allows tailoring to exact cell dimensions. It makes the
most efficient use of available space and achieves a packaging efficiency of
90 to 95 percent, the highest among battery packs. Because of the absence of
a metal can, the pouch pack has a lower weight. The main applications are
mobile phones and military devices. No standardized pouch cells exist, but
rather, each manufacturer builds to a special application.
The pouch cell is exclusively used for Li-ion and Li-ion polymer chemistries.
At the present time, it costs more to produce this cell architecture and its
reliability has not been fully proven. In addition, the energy density and load
current are slightly lower than that of conventional cell designs. The cycle life
in everyday applications is not well documented but is, at present, less than
that of the Li-ion system with conventional cell design.
A critical issue with the pouch cell is the swelling that occurs when gas is
generated during charging or discharging. Battery manufacturers insist that
Li-ion or Polymer cells do not generate gas if properly formatted, are charged
at the correct current and are kept within allotted voltage levels. When
designing the protective housing for a pouch cell, some provision for swelling
must be made. To alleviate the swelling issue when using multiple cells, it is
best not to stack pouch cells, but lay them side by side.
Figure 3-4: The pouch cell.
The pouch cell offers a simple,
flexible and lightweight
solution to battery design. This
new concept has not yet fully
matured and the manufacturing
costs are still high.
© Cadex Electronics Inc.
The pouch cell is highly sensitive to twisting. Point pressure must also be
avoided. The protective housing must be designed to protect the cell from
mechanical stress.
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Series and Parallel Configurations
In most cases, a single cell does not provide a high enough voltage and a
serial connection of several cells is needed. The metallic skin of the cell is
insulated to prevent the ‘hot’ metal cylinders from creating an electrical short
circuit against the neighboring cell.
Nickel-based cells provide a nominal cell voltage of 1.25V. A lead acid cell
delivers 2V and most Li-ion cells are rated at 3.6V. The spinel (manganese)
and Li-ion polymer systems sometimes
use 3.7V as the designated cell voltage.
This is the reason for the often
unfamiliar voltages, such as 11.1V for a
three cell pack of spinel chemistry.
Nickel-based cells are often marked
1.2V. There is no difference between a
1.2 and 1.25V cell; it is simply the
preference of the manufacturer in
marking. Whereas commercial batteries
tend to be identified with 1.2V/cell, industrial, aviation and military batteries
are still marked with the original designation of 1.25V/cell.
A five-cell nickel-based battery delivers 6V (6.25V with 1.25V/cell marking)
and a six-cell pack has 7.2V (7.5V with 1.25V/cell marking). The portable
lead acid comes in 3 cell (6V) and 6 cell (12V) formats. The Li-ion family has
either 3.6V for a single cell pack, 7.2V for a two-cell pack or 10.8V for a
three-cell pack. The 3.6V and 7.2V batteries are commonly used for mobile
phones; laptops use the larger 10.8V packs.
There has been a trend towards lower voltage batteries for light portable
devices, such as mobile phones. This was made possible through
advancements in microelectronics. To achieve the same energy with lower
voltages, higher currents are needed. With higher currents, a low internal
battery resistance is critical. This presents a challenge if protection devices are
used. Some losses through the solid-state switches of protection devices
cannot be avoided.
Packs with fewer cells in series generally perform better than those with
12 cells or more. Similar to a chain, the more links that are used, the greater
the odds of one breaking. On higher voltage batteries, precise cell matching
becomes important, especially if high load currents are drawn or if the pack is
operated in cold temperatures.
Parallel connections are used to obtain higher ampere-hour (Ah) ratings.
When possible, pack designers prefer using larger cells. This may not always
be practical because new battery chemistries come in limited sizes. Often, a
parallel connection is the only option to increase the battery rating. Paralleling
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is also necessary if pack dimensions restrict the use of larger cells. Among the
battery chemistries, Li-ion lends itself best to parallel connection.
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Protection Circuits
Most battery packs include some type of protection to safeguard battery and
equipment, should a malfunction occur. The most basic protection is a fuse
that opens if excessively high current is drawn. Some fuses open permanently
and render the battery useless once the filament is broken; other fuses are
based on a Polyswitch™, which resembles a resettable fuse. On excess
current, the Polyswitch™ creates a high resistance, inhibiting the current
flow. When the condition normalizes, the resistance of the switch reverts to
the low ON position, allowing normal operation to resume. Solid-state
switches are also used to disrupt the current. Both solid-state switches and the
Polyswitch™ have a residual resistance to the ON position during normal
operation, causing a slight increase in internal battery resistance.
A more complex protection circuit is found in intrinsically safe batteries.
These batteries are mandated for two-way radios, gas detectors and other
electronic instruments that operate in a hazardous area such as oil refineries
and grain elevators. Intrinsically safe batteries prevent explosion, should the
electronic devices malfunction while operating in areas that contain explosive
gases or high dust concentration. The protection circuit prevents excessive
current, which could lead to high heat and electric spark.
There are several levels of intrinsic safety, each serving a specific hazard
level. The requirement for intrinsic safety varies from country to country. The
purchase cost of an intrinsically safe battery is two or three times that of a
regular battery.
Commercial Li-ion packs contain one of the most exact protection circuits in
the battery industry. These circuits assure safety under all circumstances when
in the hands of the public. Typically, a Field Effect Transistor (FET) opens if
the charge voltage of any cell reaches 4.30V and a fuse activates if the cell
temperature approaches 90°C (194°F). In addition, a disconnect switch in
each cell permanently interrupts the charge current if a safe pressure threshold
of 1034 kPa (150 psi) is exceeded. To prevent the battery from
over-discharging, the control circuit cuts off the current path at low voltage,
which is typically 2.50V/cell.
The Li-ion is typically discharged to 3V/cell. The lowest ‘low-voltage’ power
cut-off is 2.5V/cell. During prolonged storage, however, a discharge below
that cut-off level is possible. Manufacturers recommend a ‘trickle’ charge to
raise such a battery gradually back up into the acceptable voltage window.
Not all chargers are designed to apply a charge once a Li-ion battery has
dipped below 2.5V/cell. A ‘wake-up’ boost will be needed to first engage the
electronic circuit, after which a gentle charge is applied to re-energize the
battery. Caution must be applied not to boost lithium-based batteries back to
life, which have dwelled at a very low voltage for a prolonged time.
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Each parallel string of cells of a Li-ion pack needs independent voltage
monitoring. The more cells that are connected in series, the more complex the
protection circuit becomes. Four cells in series is the practical limit for
commercial applications.
The internal protection circuit of a mobile phone while in the ON position has
a resistance of 50 to 100 mW. The circuit normally consists of two switches
connected in series. One is responsible for high cut-off, the other for low
cut-off. The combined resistance of these two devices virtually doubles the
internal resistance of a battery pack, especially if only one cell is used. Battery
packs powering mobile phones, for example, must be capable of delivering
high current bursts. The internal protection does, in a certain way, interfere
with the current delivery.
Some small Li-ion packs with spinel chemistry containing one or two cells
may not include an electronic protection circuit. Instead, they use a single
component fuse device. These cells are deemed safe because of small size and
low capacity. In addition, spinel is more tolerant than other systems if abused.
The absence of a protection circuit saves money, but a new problem arises.
Here is what can happen:
Mobile phone users have access to chargers that may not be approved by the
battery manufacturer. Available at low cost for car and travel, these chargers
may rely on the battery’s protection circuit to terminate at full charge.
Without the protection circuit, the battery cell voltage rises too high and
overcharges the battery. Apparently still safe, irreversible battery damage
often occurs. Heat buildup and bulging is common under these circumstances.
Such situations must be avoided at all times. The manufacturers are often at a
loss when it comes to replacing these batteries under warranty.
Li-ion batteries with cobalt electrodes, for example, require full safety
protection. A major concern arises if static electricity or a faulty charger has
destroyed the battery’s protection circuit. Such damage often causes the
solid-state switches to fuse in a permanent ON position without the user’s
knowledge. A battery with a faulty protection circuit may function normally
but does not provide the required safety. If charged beyond safe voltage limits
with a poorly designed accessory charger, the battery may heat up, then bulge
and in some cases vent with flame. Shorting such a battery can also be
hazardous.
Manufacturers of Li-ion batteries refrain from mentioning explosion. ‘Venting
with flame’ is the accepted terminology. Although slower in reaction than an
explosion, venting with flame can be very violent and inflicts injury to those
in close proximity. It can also damage the equipment to which the battery is
connected.
Most manufacturers do not sell the Li-ion cells by themselves but make them
available in a battery pack, complete with protection circuit. This precaution
is understandable when considering the danger of explosion and fire if the
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battery is charged and discharged beyond its safe limits. Most battery
assembling houses must certify the pack assembly and protection circuit
intended to be used with the manufacturer before these items are approved for
sale.
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or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
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Chapter 4: Proper Charge
Methods
To a large extent, the performance and longevity of rechargeable batteries
depends on the quality of the chargers. Battery chargers are commonly given
low priority, especially on consumer products. Choosing a quality charger
makes sense. This is especially true when considering the high cost of battery
replacements and the frustration that poorly performing batteries create. In
most cases, the extra money invested is returned because the batteries last
longer and perform more efficiently.
All About Chargers
There are two distinct varieties of
chargers: the personal chargers and
the industrial chargers. The personal
charger is sold in attractive
packaging and is offered with such
products as mobile phones, laptops
and video cameras. These chargers
are economically priced and perform
well when used for the application
intended. The personal charger offers moderate charge times.
In comparison, the industrial charger is designed for employee use and
accommodates fleet batteries. These chargers are built for repetitive use.
Available for single or multi-bay configurations, the industrial chargers are
offered from the original equipment manufacturer (OEM). In many instances,
the chargers can also be obtained from third party manufacturers. While the
OEM chargers meet basic requirements, third party manufacturers often
include special features, such as negative pulse charging, discharge function
for battery conditioning, and state-of-charge (SoC) and state-of-health (SoH)
indications. Many third party manufacturers are prepared to build low
quantities of custom chargers. Other benefits third party suppliers can offer
include creative pricing and superior performance.
Not all third party charger manufacturers meet the quality standards that the
industry demands, The buyer should be aware of possible quality and
performance compromises when purchasing these chargers at discount prices.
Some units may not be rugged enough to withstand repetitive use; others may
develop maintenance problems such as burned or broken battery contacts.
Uncontrolled over-charge is another problem of some chargers, especially
those used to charge nickel-based batteries. High temperature during charge
and standby kills batteries. Over-charging occurs when the charger keeps the
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battery at a temperature that is warm to touch (body temperature) while in
ready condition.
Some temperature rise cannot be
avoided when charging
nickel-based batteries. A
temperature peak is reached when
the battery approaches full charge.
The temperature must moderate
when the ready light appears and
the battery has switched to trickle
charge. The battery should
eventually cool to room temperature.
If the temperature does not drop and remains above room temperature, the
charger is performing incorrectly. In such a case, the battery should be
removed as soon as possible after the ready light appears. Any prolonged
trickle charging will damage the battery. This caution applies especially to the
NiMH because it cannot absorb overcharge well. In fact, a NiMH with high
trickle charge could be cold to the touch and still be in a damaging overcharge
condition. Such a battery would have a short service life.
A lithium-based battery should never get warm in a charger. If this happens,
the battery is faulty or the charger is not functioning properly. Discontinue
using this battery and/or charger.
It is best to store batteries on a shelf and apply a topping-charge before use
rather than leaving the pack in the charger for days. Even at a seemingly
correct trickle charge, nickel-based batteries produce a crystalline formation
(also referred to as ‘memory’) when left in the charger. Because of relatively
high self-discharge, a topping charge is needed before use. Most Li-ion
chargers permit a battery to remain engaged without inflicting damage.
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There are three types of chargers for nickel-based batteries. They are:
Slow Charger — Also known as ‘overnight charger’ or ‘normal charger’, the
slow-charger applies a fixed charge rate of about 0.1C (one tenth of the rated
capacity) for as long as the battery is connected. Typical charge time is 14 to
16 hours. In most cases, no full-charge detection occurs to switch the battery
to a lower charge rate at the end of the charge cycle. The slow-charger is
inexpensive and can be used for NiCd batteries only. With the need to service
both NiCd and NiMH, these chargers are being replaced with more advanced
units.
If the charge current is set correctly, a battery in a slow-charger remains
lukewarm to the touch when fully charged. In this case, the battery does not
need to be removed immediately when ready but should not stay in the
charger for more than a day. The sooner the battery can be removed after
being fully charged, the better it is.
A problem arises if a smaller battery (lower mAh) is charged with a charger
designed to service larger packs. Although the charger will perform well in
the initial charge phase, the battery starts to heat up past the 70 percent charge
level. Because there is no provision to lower the charge current or to terminate
the charge, heat-damaging over-charge will occur in the second phase of the
charge cycle. If an alternative charger is not available, the user is advised to
observe the temperature of the battery being charged and disconnect the
battery when it is warm to the touch.
The opposite may also occur when a larger battery is charged on a charger
designed for a smaller battery. In such a case, a full charge will never be
reached. The battery remains cold during charge and will not perform as
expected. A nickel-based battery that is continuously undercharged will
eventually loose its ability to accept a full charge due to memory.
Quick Charger — The so-called quick-charger, or rapid charger, is one of
the most popular. It is positioned between the slow-charger and the
fast-charger, both in terms of charging time and price. Charging takes 3 to
6 hours and the charge rate is around 0.3C. Charge control is required to
terminate the charge when the battery is ready. The well designed
quick-charger provides better service to nickel-based batteries than the
slow-charger. Batteries last longer if charged with higher currents, provided
they remain cool and are not overcharged. The quick-chargers are made to
accommodate either nickel-based or lithium-based batteries. These two
chemistries can normally not be interchanged in the same charger.
Fast Charger — The fast-charger offers several advantages over the other
chargers; the obvious one is shorter charge times. Because of the larger power
supply and the more expensive control circuits needed, the fast-charger costs
more than slower chargers, but the investment is returned in providing good
performing batteries that live longer.
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The charge time is based on the charge rate, the battery’s SoC, its rating and
the chemistry. At a 1C charge rate, an empty NiCd typically charges in a little
more than an hour. When a battery is fully charged, some chargers switch to a
topping charge mode governed by a timer that completes the charge cycle at a
reduced charge current. Once fully charged, the charger switches to trickle
charge. This maintenance charge compensates for the self-discharge of the
battery.
Modern fast-chargers commonly accommodate both NiCd and NiMH
batteries. Because of the fast-charger’s higher charge current and the need to
monitor the battery during charge, it is important to charge only batteries
specified by the manufacturer. Some battery manufacturers encode the
batteries electrically to identify their chemistry and rating. The charger then
sets the correct charge current and algorithm for the battery intended. Lead
Acid and Li-ion chemistries are charged with different algorithms and are not
compatible with the charge methods used for nickel-based batteries.
It is best to fast charge nickel-based batteries. A slow charge is known to
build up a crystalline formation on nickel-based batteries, a phenomenon that
lowers battery performance and shortens service life. The battery temperature
during charge should be moderate and the temperature peak kept as short as
possible.
It is not recommended to leave a nickel-based battery in the charger for more
than a few days, even with a correctly set trickle charge current. If a battery
must remain in a charger for operational readiness, an exercise cycle should
be applied once every month.
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Simple Guidelines
A charger designed to service NiMH batteries can also accommodate NiCd’s,
but not the other way around. A charger only made for the NiCd batteries
could overcharge the NiMH battery.
While many charge methods exist for nickel-based batteries, chargers for
lithium-based batteries are more defined in terms of charge method and
charge time. This is, in part, due to the tight charge regime and voltage
requirements demanded by these batteries. There is only one way to charge
Li-ion/Polymer batteries and the so-called ‘miracle chargers’, which claim to
restore and prolong battery life, do not exist for these chemistries. Neither
does a super-fast charging solution apply.
The pulse charge method for Li-ion has no major advantages and the voltage
peaks wreak havoc with the voltage limiting circuits. While charge times can
be reduced, some manufacturers suggest that pulse charging may shorten the
cycle life of Li-ion batteries.
Fast charge methods do not significantly decrease the charge time. A charge
rate over 1C should be avoided because such high current can induce lithium
plating. With most packs, a charge above 1C is not possible. The protection
circuit limits the amount of current the battery can accept. The lithium-based
battery has a slow metabolism and must take its time to absorb the energy.
Lead acid chargers serve industrial markets such as hospitals and health care
units. Charge times are very long and cannot be shortened. Most lead acid
chargers charge the battery in 14 hours. Because of its low energy density,
this battery type is not used for small portable devices.
In the following sections various charging needs and charging methods are
studied. The charging techniques of different chargers are examined to
determine why some perform better than others. Since fast charging rather
than slow charging is the norm today, we look at well-designed, closed loop
systems, which communicate with the battery and terminate the fast charge
when certain responses from the battery are received.
Charging the Nickel Cadmium Battery
Battery manufacturers recommend that new batteries be slow-charged for
24 hours before use. A slow charge helps to bring the cells within a battery
pack to an equal charge level because each cell self-discharges to different
capacity levels. During long storage, the electrolyte tends to gravitate to the
bottom of the cell. The initial trickle charge helps redistribute the electrolyte
to remedy dry spots on the separator that may have developed.
Some battery manufacturers do not fully form their batteries before shipment.
These batteries reach their full potential only after the customer has primed
them through several charge/discharge cycles, either with a battery analyzer
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or through normal use. In many cases, 50 to 100 discharge/charge cycles are
needed to fully form a nickel-based battery. Quality cells, such as those made
by Sanyo and Panasonic, are known to perform to full specification after as
few as 5 to 7 discharge/charge cycles. Early readings may be inconsistent, but
the capacity levels become very steady once fully primed. A slight capacity
peak is observed between 100 and 300 cycles.
Most rechargeable cells are equipped with a safety vent to release excess
pressure if incorrectly charged. The safety vent on a NiCd cell opens at
1034 to 1379 kPa (150 to 200 psi). In comparison, the pressure of a car tire is
typically 240 kPa (35 psi). With a resealable vent, no damage occurs on
venting but some electrolyte is lost and the seal may leak afterwards. When
this happens, a white powder will accumulate over time at the vent opening.
Commercial fast-chargers are
often not designed in the best
interests of the battery. This is
especially true of NiCd chargers
that measure the battery’s charge
state solely through temperature
sensing. Although simple and
inexpensive in design, charge
termination by temperature
sensing is not accurate. The
thermistors used commonly exhibit broad tolerances; their positioning with
respect to the cells are not consistent. Ambient temperatures and exposure to
the sun while charging also affect the accuracy of full-charge detection. To
prevent the risk of premature cut-off and assure full charge under most
conditions, charger manufacturers use 50°C (122°F) as the recommended
temperature cut-off. Although a prolonged temperature above 45°C (113°F) is
harmful to the battery, a brief temperature peak above that level is often
unavoidable.
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More advanced NiCd chargers sense the rate of temperature increase, defined as
dT/dt, or the change in temperature over charge time, rather than responding to an
absolute temperature (dT/dt is defined as delta Temperature / delta time). This
type of charger is kinder to the batteries than a fixed temperature cut-off, but the
cells still need to generate heat to trigger detection. To terminate the charge, a
temperature increase of 1°C (1.8°F) per minute with an absolute temperature
cut-off of 60°C (140°F) works well. Because of the relatively large mass of a cell
and the sluggish propagation of heat, the delta temperature, as this method is
called, will also enter a brief overcharge condition before the full-charge is
detected. The dT/dt method only works with fast chargers.
Harmful overcharge occurs if a fully charged battery is repeatedly inserted for
topping charge. Vehicular or base station chargers that require the removal of
two-way radios with each use are especially hard on the batteries because each
reconnection initiates a fast-charge cycle. This also applies to laptops that are
momentarily disconnected and reconnected to perform a service. Likewise, a
technician may briefly plug the laptop into the power source to check a repeater
station or service other installations. Problems with laptop batteries have also been
reported in car manufacturing plants where the workers move the laptops from car
to car, checking their functions, while momentarily plugging into the external
power source. Repetitive connection to power affects mostly ‘dumb’ nickel-based
batteries. A ‘dumb’ battery contains no electronic circuitry to communicate with
the charger. Li-ion chargers detect the SoC by voltage only and multiple
reconnections will not confuse the charging regime.
More precise full charge detection of nickel-based batteries can be achieved with
the use of a micro controller that monitors the battery voltage and terminates the
charge when a certain voltage signature occurs. A drop in voltage signifies that
the battery has reached full charge. This is known as Negative Delta V (NDV).
NDV is the recommended full-charge detection method for ‘open-lead’ NiCd
chargers because it offers a quick response time. The NDV charge detection also
works well with a partially or fully charged battery. If a fully charged battery is
inserted, the terminal voltage raises quickly, then drops sharply, triggering the
ready state. Such a charge lasts only a few minutes and the cells remain cool.
NiCd chargers based on the NDV full charge detection typically respond to a
voltage drop of 10 to 30mV per cell. Chargers that respond to a very small voltage
decrease are preferred over those that require a larger drop.
To obtain a sufficient voltage drop, the charge rate must be 0.5C and higher.
Lower than 0.5C charge rates produce a very shallow voltage decrease that is
often difficult to measure, especially if the cells are slightly mismatched. In a
battery pack that has mismatched cells, each cell reaches the full charge at a
different time and the curve gets distorted. Failing to achieve a sufficient negative
slope allows the fast-charge to continue, causing excessive heat buildup due to
overcharge. Chargers using the NDV must include other charge-termination
methods to provide safe charging under all conditions. Most chargers also observe
the battery temperature.
The charge efficiency factor of a standard NiCd is better on fast charge than slow
charge. At a 1C charge rate, the typical charge efficiency is 1.1 or 91 percent. On
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an overnight slow charge (0.1C), the efficiency drops to 1.4 or 71 percent.
At a rate of 1C, the charge time of a NiCd is slightly longer than 60 minutes
(66 minutes at an assumed charge efficiency of 1.1). The charge time on a battery
that is partially discharged or cannot hold full capacity due to memory or other
degradation is shorter accordingly. At a 0.1C charge rate, the charge time of an
empty NiCd is about 14 hours, which relates to the charge efficiency of 1.4.
During the first 70 percent of the charge cycle, the charge efficiency of a NiCd
battery is close to 100 percent. Almost all of the energy is absorbed and the
battery remains cool. Currents of several times the C-rating can be applied to a
NiCd battery designed for fast charging without causing heat build-up. Ultra-fast
chargers use this unique phenomenon and charge a battery to the 70 percent
charge level within a few minutes. The charge continues at a lower rate until the
battery is fully charged.
Once the 70 percent charge threshold is passed, the battery gradually loses ability
to accept charge. The cells start to generate gases, the pressure rises and the
temperature increases. The charge acceptance drops further as the battery reaches
80 and 90 percent SoC. Once full charge is reached, the battery goes into
overcharge. In an attempt to gain a few extra capacity points, some chargers allow
a measured amount of overcharge. Figure 4-1 illustrates the relationship of cell
voltage, pressure and temperature while a NiCd is being charged.
Ultra-high capacity NiCd batteries tend to heat up more than the standard NiCd if
charged at 1C and higher. This is partly due to the higher internal resistance of the
ultra-high capacity battery. Optimum charge performance can be achieved by
applying higher current at the initial charge stage, then tapering it to a lower rate
as the charge acceptance decreases. This avoids excess temperature rise and yet
assures fully charged batteries.
Figure 4-1: Charge characteristics of a NiCd cell.
These cell voltage, pressure and temperature characteristics are similar in a NiMH
cell.
Interspersing discharge pulses between charge pulses improves the charge
acceptance of nickel-based batteries. Commonly referred to as ‘burp’ or ‘reverse
load’ charge, this charge method promotes high surface area on the electrodes,
resulting in enhanced performance and increased service life. Reverse load also
improves fast charging because it helps to recombine the gases generated during
charge. The result is a cooler and more effective charge than with conventional
DC chargers.
Charging with the reverse load method minimizes crystalline formation. The US
Army Electronics Command in Fort Monmouth, NJ, USA, had done extensive
research in this field and has published the results. (See Figure 10-1, Crystalline
formation on NiCd cell). Research conducted in Germany has shown that the
reverse load method adds 15 percent to the life of the NiCd battery.
After full charge, the NiCd battery is maintained with a trickle charge to
compensate for the self-discharge. The trickle charge for a NiCd battery ranges
between 0.05C and 0.1C. In an effort to reduce the memory phenomenon, there is
a trend towards lower trickle charge currents.
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Charging the Nickel-Metal Hydride
Battery
Chargers for NiMH batteries are very similar to those of the NiCd system but
the electronics is generally more complex. To begin with, the NiMH produces
a very small voltage drop at full charge. This NDV is almost non-existent at
charge rates below 0.5C and elevated temperatures. Aging and cell mismatch
works further against the already minute voltage delta. The cell mismatch gets
worse with age and increased cycle count, which makes the use of the NDV
increasingly more difficult.
The NDV of a NiMH charger must respond to a voltage drop of 16mV or less.
Increasing the sensitivity of the charger to respond to the small voltage drop
often terminates the fast charge by error halfway through the charge cycle.
Voltage fluctuations and noise induced by the battery and charger can fool the
NDV detection circuit if set too precisely.
The popularity of the NiMH battery has introduced many innovative charging
techniques. Most of today’s NiMH fast chargers use a combination of NDV,
voltage plateau, rate-of-temperature-increase (dT/dt), temperature threshold
and timeout timers. The charger utilizes whatever comes first to terminate the
fast-charge.
NiMH batteries which use the NDV method or the thermal cut-off control
tend to deliver higher capacities than those charged by less aggressive
methods. The gain is approximately 6 percent on a good battery. This capacity
increase is due to the brief overcharge to which the battery is exposed. The
negative aspect is a shorter cycle life. Rather than expecting 350 to
400 service cycles, this pack may be exhausted with 300 cycles.
Similar to NiCd charge methods, most NiMH fast-chargers work on the
rate-of-temperature-increase (dT/dt). A temperature raise of 1°C (1.8°F) per
minute is commonly used to terminate the charge. The absolute temperature
cut-off is 60°C (140°F). A topping charge of 0.1C is added for about
30 minutes to maximize the charge. The continuous trickle charge that
follows keeps the battery in full charge state.
Applying an initial fast charge of 1C works well. Cooling periods of a few
minutes are added when certain voltage peaks are reached. The charge then
continues at a lower current. When reaching the next charge threshold, the
current steps down further. This process is repeated until the battery is fully
charged.
Known as ‘step-differential charge’, this charge method works well with
NiMH and NiCd batteries. The charge current adjusts to the SoC, allowing
high current at the beginning and more moderate current towards the end of
charge. This avoids excessive temperature build-up towards the end of the
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charge cycle when the battery is less capable of accepting charge.
NiMH batteries should be rapid charged rather than slow charged. The
amount of trickle charge applied to maintain full charge is especially critical.
Because NiMH does not absorb overcharge well, the trickle charge must be
set lower than that of the NiCd. The recommended trickle charge for the
NiMH battery is a low 0.05C. This is why the original NiCd charger cannot
be used to charge NiMH batteries. The lower trickle charge rate is acceptable
for the NiCd.
It is difficult, if not impossible, to slow-charge a NiMH battery. At a C-rate of
0.1C and 0.3C, the voltage and temperature profiles fail to exhibit defined
characteristics to measure the full charge state accurately and the charger must
depend on a timer. Harmful overcharge can occur if a partially or fully
charged battery is charged on a charger with a fixed timer. The same occurs if
the battery has lost charge acceptance due to age and can only hold 50 percent
of charge. A fixed timer that delivers a 100 percent charge each time without
regard to the battery condition would ultimately apply too much charge.
Overcharge could occur even though the NiMH battery feels cool to the
touch.
Some lower-priced chargers may not apply a fully saturated charge. On these
economy chargers, the full-charge detection may occur immediately after a
given voltage peak is reached or a temperature threshold is detected. These
chargers are commonly promoted on the merit of short charge time and
moderate price.
Figure 4-2 summarizes the characteristics of the slow charger, quick
charger and fast charger. A higher charge current allows better full-charge
detection.
Charge Typical
C-rate charge
time
Maximum
permissible
charge
temperatures
Charge termination
method
0°C to 45°C
(32°F to 113°F)
Fixed timer. Subject to
overcharge. Remove
battery when charged.
Quick 0.3-0.5C 4h
Charger
10°C to 45°C
(50°F to 113°F)
NDV set to 10mV/cell,
uses voltage plateau,
absolute temperature
and time-out-timer. (At
0.3C, dT/dt fails to raise
the temperature
sufficiently to terminate
the charge.)
Fast
1C
Charger
10°C to 45°C
(50°F to 113°F)
NDV responds to higher
settings; uses dT/dt,
voltage plateau absolute
temperature and
time-out-timer
Slow
0.1C
Charger
14h
1h+
Figure 4-2: Characteristics of various charger types.
These values also apply to NiMH and NiCd cells.
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Charging the Lead Acid Battery
The charge algorithm for lead acid batteries differs from nickel-based chemistry
in that voltage limiting rather than current limiting is used. Charge time of a
sealed lead acid (SLA) is 12 to 16 hours. With higher charge currents and
multi-stage charge methods, charge time can be reduced to 10 hours or less.
SLAs cannot be fully charged as quickly as nickel-based systems.
A multi-stage charger applies constant-current charge, topping charge and float
charge (see Figure 4-3). During the constant current charge, the battery charges
to 70 percent in about five hours; the remaining 30 percent is completed by the
slow topping charge. The topping charge lasts another five hours and is essential
for the well-being of the battery. This can be compared to a little rest after a
good meal before resuming work. If the battery is not completely saturated, the
SLA will eventually lose its ability to accept a full charge and the performance
of the battery is reduced. The third stage is the float charge, which compensates
for the self-discharge after the battery has been fully charged.
Figure 4-3: Charge stages of a lead acid battery.
A multi-stage charger applies constant-current charge, topping charge and float
charge.
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Correctly setting the cell-voltage limit is critical. A typical voltage limit is from
2.30V to 2.45V. If a slow charge is acceptable, or the room temperature may
exceed 30°C (86°F), the recommended voltage limit is 2.35V/cell. If a faster
charge is required, and the room temperature will remain below 30°C, 2.40 to
2.45V/cell may be used. Figure 4-4 compares the advantages and disadvantages
of the different voltage settings.
2.30V to 2.35V/cell
Advantage
Maximum service life; battery
remains cool during charge;
ambient charge temperature
may exceed 30°C (86°F).
Disadvantage Slow charge time; capacity
readings may be low and
inconsistent. If no periodic
topping charge is applied,
under-charge conditions
(sulfation) may occur, which
can lead to unrecoverable
capacity loss.
2.40V to 2.45V/cell
Faster charge times; higher
and more consistent capacity
readings; less subject to
damage due to under-charge
condition.
Battery life may be reduced
due to elevated battery
temperature while charging. A
hot battery may fail to reach
the cell voltage limit, causing
harmful over charge.
Figure 4-4: Effects of charge voltage on a plastic SLA battery.
Large VRLA and the cylindrical Hawker cell may have different requirements.
The charge voltage limit indicated in Figure 4-4 is a momentary voltage peak
and the battery cannot dwell on that level. This voltage crest is only used when
applying a full charge cycle to a battery that has been discharged. Once fully
charged and at operational readiness, a float charge is applied, which is held
constant at a lower voltage level. The recommended float charge voltage of most
low-pressure lead acid batteries is between 2.25 to 2.30V/cell. A good
compromise is 2.27V.
The optimal float charge voltage shifts with temperature. A higher temperature
demands slightly lower voltages and a lower temperature demands higher
voltages. Chargers that are exposed to large temperature fluctuations are
equipped with temperature sensors to optimize the float voltage.
Regardless of how well the float voltage may be compensated, there is always a
compromise. The author of a paper in a battery seminar explained that charging
a sealed lead acid battery using the traditional float charge techniques is like
'dancing on the head of a pin'. The battery wants to be fully charged to avoid
sulfation on the negative plate, but does not want to be over-saturated which
causes grid corrosion on the positive plate. In addition to grid corrosion, too high
a float charge contributes to loss of electrolyte.
Differences in the aging of the cells create another challenge in finding the
optimum float charge voltage. With the development of air pockets within the
cells over time, some batteries exhibit hydrogen evolution from overcharging.
Others undergo oxygen recombination in an almost starved state. Since the cells
are connected in series, controlling the individual cell voltages during charge is
virtually impossible. If the applied cell voltage is too high or too low for a given
cell, the weaker cell deteriorates further and its condition becomes more
pronounced with time. Companies have developed cell-balancing devices that
correct some of these problems but these devices can only be applied if access to
individual cells is possible.
A ripple voltage imposed on the charge voltage also causes problems for lead
acid batteries, especially the larger VRLA. The peak of the ripple voltage
constitutes an overcharge, causing hydrogen evolution; the valleys induce a brief
discharge causing a starved state. Electrolyte depletion may be the result.
Much has been said about pulse charging lead acid batteries. Although there are
obvious benefits of reduced cell corrosion, manufacturers and service
technicians are not in agreement regarding the benefit of such a charge method.
Some advantages are apparent if pulse charging is applied correctly, but the
results are non-conclusive.
Whereas the voltage settings in Figure 4-4 apply to low-pressure lead acid
batteries with a pressure relief valve setting of about 34 kPa (5 psi), the
cylindrical SLA by Hawker requires higher voltage settings. These voltage limits
should be set according to the manufacturer’s specifications. Failing to apply the
recommended voltage threshold for these batteries causes a gradual decrease in
capacity due to sulfation. Typically, the Hawker cell has a pressure relief setting
of 345 kPa (50 psi). This allows some recombination of the gases during charge.
An SLA must be stored in a charged state. A topping charge should be applied
every six months to avoid the voltage from dropping below 2.10V/cell. The
topping charge requirements may differ with cell manufacturers. Always follow
the time intervals recommended by the manufacturer.
By measuring the open cell voltage while in storage, an approximate
charge-level indication can be obtained. A voltage of 2.11V, if measured at room
temperature, reveals that the cell has a charge of 50 percent and higher. If the
voltage is at or above this threshold, the battery is in good condition and only
needs a full charge cycle prior to use. If the voltage drops below 2.10V, several
discharge/charge cycles may be required to bring the battery to full performance.
When measuring the terminal voltage of any cell, the storage temperature should
be observed. A cool battery raises the voltage slightly and a warm one lowers it.
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Plastic SLA batteries arriving from vendors with less than 2.10V per cell are
rejected by some buyers who inspect the battery during quality control. Low
voltage suggests that the battery may have a soft short, a defect that cannot be
corrected with cycling. Although cycling may increase the capacity of these
batteries, the extra cycles compromise the service life of the battery.
Furthermore, the time and equipment required to make the battery fully
functional adds to operational costs.
The Hawker cell can be stored at voltages as low as 1.81V. However, when
reactivating the cells, a higher than normal charge voltage may be required to
convert the large sulfite crystals back to good active material.
Caution: When charging a lead acid battery with over-voltage, current
limiting must be applied once the battery starts to draw full current. Always
set the current limit to the lowest practical setting and observe the battery
voltage and temperature during the procedure. If the battery does not accept a
normal charge after 24 hours under elevated voltage, a return to normal
condition is unlikely.
The price of the Hawker cell is slightly higher than that of the plastic
equivalent, but lower than the NiCd. Also known as the ‘Cyclone’, this cell is
wound similar to a cylindrical NiCd. This construction improves the cell’s
stability and provides higher discharge currents when compared to the flat
plate SLA. Because of its relatively low self-discharge, Hawker cells are well
suited for defibrillators that are used on standby mode.
Lead acid batteries are preferred for UPS systems. During prolonged float
charge, a periodic topping charge, also known as an ‘equalizing charge’, is
recommended to fully charge the plates and prevent sulfation. An equalizing
charge raises the battery voltage for several hours to a voltage level above that
specified by the manufacturer. Loss of electrolyte through elevated
temperature may occur if the equalizing charge is not administered correctly.
Because no liquid can be added to the SLA and VRLA systems, a reduction of
the electrolyte will cause irreversible damage. Manufacturers and service
personnel are often divided on the benefit of the equalizing charge.
Some exercise, or brief periodic discharge, is believed to prolong battery life
of lead acid systems. If applied once a month as part of an exercising
program, the depth of discharge should only be about 10 percent of its total
capacity. A full discharge as part of regular maintenance is not recommended
because each deep discharge cycle robs service life from the battery.
More experiments are needed to verify the benefit of exercising lead acid
batteries. Again, manufacturers and service technicians express different
views on how preventive maintenance should be carried out. Some experts
prefer a topping charge while others recommend scheduled discharges. No
scientific data is available on the benefit of frequent shallow discharges as
opposed to fewer deep discharges or discharge pulses.
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Disconnecting the float charge while the VRLA is on standby is another
method of prolonging battery life. From time-to-time, a topping charge is
applied to replenish the energy lost through self-discharge. This is said to
lower cell corrosion and prolong battery life. In essence, the battery is kept as
if it was in storage. This only works for applications that do not draw a load
current during standby. In many applications, the battery acts as an energy
buffer and needs to be under continuous charge.
Important: In case of rupture, leaking electrolyte or any other cause of
exposure to the electrolyte, flush with water immediately. If eye exposure
occurs, flush with water for 15 minutes and consult a physician immediately.
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Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article:
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Charging the Lithium Ion Battery
The Li-ion charger is a voltage-limiting device similar to the lead acid battery
charger. The difference lies in a higher voltage per cell, tighter voltage tolerance
and the absence of trickle or float charge when full charge is reached.
While the lead acid battery offers some flexibility in terms of voltage cut-off,
manufacturers of Li-ion cells are very strict on setting the correct voltage. When
the Li- ion was first introduced, the graphite system demanded a charge voltage
limit of 4.10V/cell. Although higher voltages deliver increased energy densities,
cell oxidation severely limited the service life in the early graphite cells that
were charged above the 4.10V/cell threshold. This effect has been solved with
chemical additives. Most commercial Li-ion cells can now be charged to 4.20V.
The tolerance on all Li-ion batteries is a tight +/-0.05V/cell.
Industrial and military Li-ion batteries designed for maximum cycle life use an
end-of-charge voltage threshold of about 3.90V/cell. These batteries are rated
lower on the watt-hour-per-kilogram scale, but longevity takes precedence over
high energy density and small size.
The charge time of all Li-ion batteries, when charged at a 1C initial current, is
about 3 hours. The battery remains cool during charge. Full charge is attained
after the voltage has reached the upper voltage threshold and the current has
dropped and leveled off at about 3 percent of the nominal charge current.
Increasing the charge current on a Li-ion charger does not shorten the charge
time by much. Although the voltage peak is reached quicker with higher current,
the topping charge will take longer. Figure 4-5 shows the voltage and current
signature of a charger as the Li-ion cell passes through stage one and two.
Some chargers claim to fast-charge a Li-ion battery in one hour or less. Such a
charger eliminates stage 2 and goes directly to ‘ready’ once the voltage threshold
is reached at the end of stage 1. The charge level at this point is about
70 percent. The topping charge typically takes twice as long as the initial charge.
No trickle charge is applied because the Li-ion is unable to absorb overcharge.
Trickle charge could cause plating of metallic lithium, a condition that renders
the cell unstable. Instead, a brief topping charge is applied to compensate for the
small amount of self-discharge the battery and its protective circuit consume.
Depending on the charger and the self-discharge of the battery, a topping charge
may be implemented once every 500 hours or 20 days. Typically, the charge
kicks in when the open terminal voltage drops to 4.05V/cell and turns off when
it reaches 4.20V/cell again.
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Figure 4-5: Charge stages of a Li-ion battery.
Increasing the charge current on a Li-ion charger does not shorten the charge
time by much. Although the voltage peak is reached quicker with higher current,
the topping charge will take longer.
What if a battery is inadvertently overcharged? Li-ion batteries are designed to
operate safely within their normal operating voltage but become increasingly
unstable if charged to higher voltages. On a charge voltage above 4.30V, the cell
causes lithium metal plating on the anode. In addition, the cathode material
becomes an oxidizing agent, loses stability and releases oxygen. Overcharging
causes the cell to heat up.
Much attention has been placed on the safety of the Li-ion battery. Commercial
Li-ion battery packs contain a protection circuit that prevents the cell voltage
from going too high while charging. The typical safety threshold is set to
4.30V/cell. In addition, temperature sensing disconnects the charge if the
internal temperature approaches 90°C (194°F). Most cells feature a mechanical
pressure switch that permanently interrupts the current path if a safe pressure
threshold is exceeded. Internal voltage control circuits cut off the battery at low
and high voltage points.
Exceptions are made on some spinel (manganese) packs containing one or two
small cells. On overcharge, this chemistry produces minimal lithium plating on
the anode because most metallic lithium has been removed from the cathode
during normal charging. The cathode material remains stable and does not
generate oxygen unless the cell gets extremely hot.
Important: In case of rupture, leaking electrolyte or any other cause of exposure
to the electrolyte, flush with water immediately. If eye exposure occurs, flush
with water for 15 minutes and consult a physician immediately.
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Charging the Lithium Polymer Battery
The charge process of a Li-Polymer is similar to that of the Li-ion. Li-Polymer
uses dry electrolyte and takes 3 to 5 hours to charge. Li-ion polymer with gelled
electrolyte, on the other hand, is almost identical to that of Li-ion. In fact, the
same charge algorithm can be applied. With most chargers, the user does not need
to know whether the battery being charged is Li-ion or Li-ion polymer.
Almost all commercial batteries sold under the so-called ‘Polymer’ category are a
variety of the Li-ion polymer using some sort of gelled electrolyte. A low-cost dry
polymer battery operating at ambient temperatures is still some years away.
Charging at High and Low Temperatures
Rechargeable batteries can be used under a reasonably wide temperature range.
This, however, does not automatically mean that the batteries can also be charged
at these temperature conditions. While the use of batteries under hot or cold
conditions cannot always be avoided, recharging time is controlled by the user.
Efforts should be made to charge the batteries only at room temperatures.
In general, older battery technologies such as the NiCd are more tolerant to
charging at low and high temperatures than the more advanced systems.
Figure 4-6 indicates the permissible slow and fast charge temperatures of the
NiCd, NiMH, SLA and Li-ion.
Slow Charge (0.1)
Fast Charge (0.5-1C)
Nickel Cadmium
0°C to 45°C (32°F to 113°F) 5°C to 45°C (41°F to 113°F)
Nickel-Metal
Hydride
0°C to 45°C (32°F to 113°F)
Lead Acid
0°C to 45°C (32°F to 113°F) 5C° to 45°C (41°F to 113°F)
Lithium Ion
0°C to 45°C (32°F to 113°F) 5C° to 45°C (41°F to 113°F)
10C° to 45°C (50°F to
113°F)
Figure 4-6: Permissible temperature limits for various batteries.
Older battery technologies are more tolerant to charging at extreme temperatures
than newer, more advanced systems.
NiCd batteries can be fast-charged in an hour or so, however, such a fast charge
can only be applied within temperatures of 5°C and 45°C (41°F and 113°F). More
moderate temperatures of 10°C to 30°C (50°F to 86°F) produce better results.
When charging a NiCd below 5°C (41°F), the ability to recombine oxygen and
hydrogen is greatly reduced and pressure build up occurs as a result. In some
cases, the cells vent, releasing oxygen and hydrogen. Not only do the escaping
gases deplete the electrolyte, hydrogen is highly flammable!
Chargers featuring NDV to terminate full-charge provide some level of protection
when fast-charging at low temperatures. Because of the battery’s poor charge
acceptance at low temperatures, the charge energy is turned into oxygen and to a
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lesser amount hydrogen. This reaction causes cell voltage drop, terminating the
charge through NDV detection. When this occurs, the battery may not be fully
charged, but venting is avoided or minimized.
To compensate for the slower reaction at temperatures below 5°C, a low charge
rate of 0.1C must be applied. Special charge methods are available for charging at
cold temperatures. Industrial batteries that need to be fast-charged at low
temperatures include a thermal blanket that heats the battery to an acceptable
temperature. Among commercial batteries, the NiCd is the only battery that can
accept charge at extremely low temperatures.
Charging at high temperatures reduces the oxygen generation. This reduces the
NDV effect and accurate full-charge detection using this method becomes
difficult. To avoid overcharge, charge termination by temperature measurement
becomes more practical.
The charge acceptance of a NiCd at higher temperatures is drastically reduced. A
battery that provides a capacity of 100 percent if charged at moderate room
temperature can only accept 70 percent if charged at 45°C (113°F), and 45 percent
if charged at 60°C (140°F) (see Figure 4-7). Similar conditions apply to the NiMH
battery. This demonstrates the typically poor summer performance of vehicular
mounted chargers using nickel-based batteries.
Another reason for poor battery performance, especially if charged at high
ambient temperatures, is premature charge cutoff. This is common with chargers
that use absolute temperature to terminate the fast charge. These chargers read the
SoC on battery temperature alone and are fooled when the room temperature is
high. The battery may not be fully charged, but a timely charge cut-off protects
the battery from damage due to excess heat.
The NiMH is less forgiving than the NiCd if charged under high and low
temperatures. The NiMH cannot be fast charged below 10°C (45°F), neither can it
be slow charged below 0°C (32°F). Some industrial chargers adjust the charge rate
to prevailing temperatures. Price sensitivity on consumer chargers does not permit
elaborate temperature control features.
Figure 4-7: Effects of temperature on NiCd charge acceptance.
Charge acceptance is much reduced at higher temperatures. NiMH cells follow a
similar pattern.
The lead acid battery is reasonably forgiving when it comes to temperature
extremes, as in the case of car batteries. Part of this tolerance is credited to the
sluggishness of the lead acid battery. A full charge under ten hours is difficult, if
not impossible. The recommended charge rate at low temperature is 0.3C.
Figure 4-8 indicates the optimal peak voltage at various temperatures when
recharging and float charging an SLA battery. Implementing temperature
compensation on the charger to adjust to temperature extremes prolongs the
battery life by up to 15 percent. This is especially true when operating at higher
temperatures.
An SLA battery should never be allowed to freeze. If this were to occur, the
battery would be permanently damaged and would only provide a few cycles
when it returned to normal temperature.
0°C (32°F)
25°C (77°F)
40°C (104°F)
Voltage limit on
recharge
2.55V/cell
2.45V/cell
2.35V/cell
Continuous float
voltage
2.35V/cell or
lower
2.30V/cell or
lower
2.25V/cell or
lower
Figure 4-8: Recommended voltage limits on recharge and float charge of SLAs.
These voltage limits should be applied when operating at temperature extremes.
To improve charge acceptance of SLA batteries in colder temperatures, and avoid
thermal runaway in warmer temperatures, the voltage limit of a charger should be
compensated by approximately 3mV per cell per degree Celsius. The voltage
adjustment has a negative coefficient, meaning that the voltage threshold drops as
the temperature increases. For example, if the voltage limit is set to 2.40V/cell at
20°C, the setting should be lowered to 2.37V/cell at 30°C and raised to 2.43V/cell
at 10°C. This represents a 30mV correction per cell per 10 degrees Celsius.
The Li-ion batteries offer good cold and hot temperature charging performance.
Some cells allow charging at 1C from 0°C to 45°C (32°F to 113°F). Most Li-ion
cells prefer a lower charge current when the temperature gets down to 5°C (41°F)
or colder. Charging below freezing must be avoided because plating of lithium
metal could occur.
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Ultra-fast Chargers
Some charger manufacturers claim amazingly short charge times of
30 minutes or less. With well-balanced cells and operating at moderate room
temperatures, NiCd batteries designed for fast charging can indeed be charged
in a very short time. This is done by simply dumping in a high charge current
during the first 70 percent of the charge cycle. Some NiCd batteries can take
as much a 10C, or ten times the rated current. Precise SoC detection and
temperature monitoring are essential.
The high charge current must be reduced to lower levels in the second phase
of the charge cycle because the efficiency to absorb charge is progressively
reduced as the battery moves to a higher SoC. If the charge current remains
too high in the later part of the charge cycle, the excess energy turns into heat
and pressure. Eventually venting occurs, releasing hydrogen gas. Not only do
the escaping gases deplete the electrolyte, they are also highly flammable!
Several manufacturers offer chargers that claim to fully charge NiCd batteries
in half the time of conventional chargers. Based on pulse charge technology,
these chargers intersperse one or several brief discharge pulses between each
charge pulse. This promotes the recombination of oxygen and hydrogen
gases, resulting in reduced pressure buildup and a lower cell temperature.
Ultra-fast-chargers based on this principle can charge a nickel-based battery
in a shorter time than regular chargers, but only to about a 90 percent SoC. A
trickle charge is needed to top the charge to 100 percent.
Pulse chargers are known to reduce the crystalline formation (memory) of
nickel-based batteries. By using these chargers, some improvement in battery
performance can be realized, especially if the battery is affected by memory.
The pulse charge method does not replace a periodic full discharge. For more
severe crystalline formation on nickel-based batteries, a full discharge or
recondition cycle is recommended to restore the battery.
Ultra-fast charging can only be applied to healthy batteries and those designed
for fast charging. Some cells are simply not built to carry high current and the
conductive path heats up. The battery contacts also take a beating if the
current handling of the spring-loaded plunger contacts is underrated. Pressing
against a flat metal surface, these contacts may work well at first, and then
wear out prematurely. Often, a fine and almost invisible crater appears on the
tip of the contact, which causes a high resistive path or forms an isolator. The
heat generated by a bad contact can melt the plastic.
Another problem with ultra-fast charging is servicing aged batteries that
commonly have high internal resistance. Poor conductivity turns into heat,
which further deteriorates the cells. Battery packs with mismatched cells pose
another challenge. The weak cells holding less capacity are charged before
those with higher capacity and start to heat up. This process makes them
vulnerable to further damage.
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Many of today’s fast chargers are designed for the ideal battery. Charging less
than perfect specimens can create such a heat buildup that the plastic housing
starts to distort. Provisions must be made to accept special needs batteries,
albeit at lower charging speeds. Temperature sensing is a prerequisite.
The ideal ultra-fast charger first checks the battery type, measures its SoH and
then applies a tolerable charge current. Ultra-high capacity batteries and those
that have aged are identified, and the charge time is prolonged because of
higher internal resistance. Such a charger would provide due respect to those
batteries that still perform satisfactorily but are no longer ‘spring chickens’.
The charger must prevent excessive temperature build-up. Sluggish heat
detection, especially when charging takes place at a very rapid pace, makes it
easy to overcharge a battery before the charge is terminated. This is especially
true for chargers that control fast charge using temperature sensing alone. If
the temperature rise is measured right on the skin of the cell, reasonably
accurate SoC detection is possible. If done on the outside surface of the
battery pack, further delays occur. Any prolonged exposure to a temperature
of 45°C (113°F) harms the battery.
New charger concepts are being studied which regulate the charge current
according to the battery's charge acceptance. On the initial charge of an empty
battery when the charge acceptance is high and little gas is generated, a very
high charge current can be applied. Towards the end of a charge, the current is
tapered down.
Charge IC Chips
Newer battery systems demand more complex chargers than batteries with
older chemistries. With today’s charge IC chips, designing a charger has been
simplified. These chips apply proven charge algorithms and are capable of
servicing all major battery chemistries. As the price of these chips decreases,
design engineers make more use of this product. With the charge IC chip, an
engineer can focus entirely on the portable equipment rather than devoting
time to developing a charging circuit.
The charge IC chips have some limitations, however. The charge algorithm is
fixed and does not allow fine-tuning. If a trickle charge is needed to raise a
Li-ion that has dropped below 2.5V/cell to its normal operating voltage, the
charge IC may not be able to perform this function. Similarly, if an ultra-fast
charge is needed for nickel-based batteries, the charge IC applies a fixed
charge current and does not take into account the SoH of the battery.
Furthermore, a temperature compensated charge would be difficult to
administer if the IC chips do not provide this feature.
Using a small micro controller is an alternative to selecting an off-the-shelf
charge IC. The hardware cost is about the same. When opting for the micro
controller, custom firmware will be needed. Some extra features can be added
with little extra cost. They are fast charging based on the SoH of the battery.
Ambient temperatures can also be taken into account. Whether an IC chip or
micro controller is used, peripheral components are required consisting of
solid-state switches and a power supply.
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Chapter 5: Discharge Methods
The purpose of a battery is to store energy and release it at the appropriate
time in a controlled manner. Being capable of storing a large amount of
energy is one thing; the ability to satisfy the load demands is another. The
third criterion is being able to deliver all available energy without leaving
precious energy behind when the equipment cuts off.
In this chapter, we examine how different discharge methods can affect the
deliverance of power. Further, we look at the load requirements of various
portable devices and evaluate the performance of each battery chemistry in
terms of discharge.
C-rate
The charge and discharge current of a battery is measured in C-rate. Most
portable batteries, with the exception of the lead acid, are rated at 1C. A
discharge of 1C draws a current equal to the rated capacity. For example, a
battery rated at 1000mAh provides 1000mA for one hour if discharged at 1C
rate. The same battery discharged at 0.5C provides 500mA for two hours. At
2C, the same battery delivers 2000mA for 30 minutes. 1C is often referred to
as a one-hour discharge; a 0.5C would be a two-hour, and a 0.1C a 10 hour
discharge.
The capacity of a battery is commonly measured with a battery analyzer. If
the analyzer’s capacity readout is displayed in percentage of the nominal
rating, 100 percent is shown if 1000mA can be drawn for one hour from a
battery that is rated at 1000mAh. If the battery only lasts for 30 minutes
before cut-off, 50 percent is indicated. A new battery sometimes provides
more than 100 percent capacity. In such a case, the battery is conservatively
rated and can endure a longer discharge time than specified by the
manufacturer.
When discharging a battery with a battery analyzer that allows setting
different discharge C-rates, a higher capacity reading is observed if the battery
is discharged at a lower C-rate and vice versa. By discharging the 1000mAh
battery at 2C, or 2000mA, the analyzer is scaled to derive the full capacity in
30 minutes. Theoretically, the capacity reading should be the same as a slower
discharge, since the identical amount of energy is dispensed, only over a
shorter time. Due to energy loss that occurs inside the battery and a drop in
voltage that causes the battery to reach the low-end voltage cut-off sooner, the
capacity reading is lower and may be 97 percent. Discharging the same
battery at 0.5C, or 500mA over two hours would increase the capacity reading
to about 103 percent.
The discrepancy in capacity readings with different C-rates largely depends
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on the internal resistance of the battery. On a new battery with a good load
current characteristic or low internal resistance, the difference in the readings
is only a few percentage points. On a battery exhibiting high internal
resistance, the difference in capacity readings could swing plus/minus
10 percent or more.
One battery that does not perform well at a 1C discharge rate is the SLA. To
obtain a practical capacity reading, manufacturers commonly rate these
batteries at 0.05C or 20 hour discharge. Even at this slow discharge rate, it is
often difficult to attain 100 percent capacity. By discharging the SLA at a
more practical 5h discharge (0.2C), the capacity readings are correspondingly
lower. To compensate for the different readings at various discharge currents,
manufacturers offer a capacity offset.
Applying the capacity offset does not improve battery performance; it merely
adjusts the capacity calculation if discharged at a higher or lower C-rate than
specified. The battery manufacturer determines the amount of capacity offset
recommended for a given battery type.
Li-ion/polymer batteries are electronically protected against high discharge
currents. Depending on battery type, the discharge current is limited
somewhere between 1C and 2C. This protection makes the Li-ion unsuitable
for biomedical equipment, power tools and high-wattage transceivers. These
applications are commonly reserved for the NiCd battery.
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Depth of Discharge
The typical end-of-discharge voltage for nickel-based batteries is 1V/cell. At that
voltage level, about 99 percent of the energy is spent and the voltage starts to
drop rapidly if the discharge continues. Discharging beyond the cut-off voltage
must be avoided, especially under heavy load.
Since the cells in a battery pack cannot be perfectly matched, a negative voltage
potential (cell reversal) across a weaker cell occurs if the discharge is allowed to
continue beyond the cut-off point. The larger the number of cells connected in
series, the greater the likelihood of this occurring.
A NiCd battery can tolerate a limited amount of cell reversal, which is typically
about 0.2V. During that time, the polarity of the positive electrode is reversed.
Such a condition can only be sustained for a brief moment because hydrogen
evolution occurs on the positive electrode. This leads to pressure build-up and
cell venting.
If the cell is pushed further into voltage reversal, the polarity of both electrodes is
being reversed, resulting in an electrical short. Such a fault cannot be corrected
and the pack will need to be replaced.
On battery analyzers that apply a secondary discharge (recondition), the current is
controlled to assure that the maximum allowable current, while in sub-discharge
range, does not exceed a safe limit. Should a cell reversal develop, the current
would be low enough as not to cause damage. A cell breakdown through
recondition is possible on a weak or aged pack.
If the battery is discharged at a rate higher than 1C, the more common
end-of-discharge point of a nickel-based battery is 0.9V/cell. This is done to
compensate for the voltage drop induced by the internal resistance of the cell, the
wiring, protection devices and contacts of the pack. A lower cut-off point also
delivers better battery performance at cold temperatures.
The recommended end-of-discharge voltage for the SLA is 1.75V/cell. Unlike the
preferred flat discharge curve of the NiCd, the SLA has a gradual voltage drop
with a rapid drop towards the end of discharge (see Figure 5-1). Although this
steady decrease in voltage is a disadvantage, it has a benefit because the voltage
level can be utilized to display the state-of-charge (SoC) of a battery. However,
the voltage readings fluctuate with load and the SoC readings are inaccurate.
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Figure 5-1: Discharge characteristics of NiCd, NiMH and SLA batteries.
While voltage readings to measure the SoC are not practical on nickel-based
batteries, the SLA enables some level of indication as to the SoC.
°C (77°F) with respect to the depth of discharge is:
● 150 – 200 cycles with 100 percent depth of discharge (full discharge)
● 400 – 500 cycles with 50 percent depth of discharge (partial discharge)
● 1000 and more cycles with 30 percent depth of discharge
(shallow discharge)
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The SLA should not be discharged beyond 1.75V per cell, nor can it be stored
in a discharged state. The cells of a discharged SLA sulfate, a condition that
renders the battery useless if left in that state for a few days.
The Li-ion typically discharges to 3.0V/cell. The spinel and coke versions can
be discharged to 2.5V/cell. The lower end-of-discharge voltage gains a few
extra percentage points. Since the equipment manufacturers cannot specify
which battery type may be used, most equipment is designed for a three-volt
cut-off.
Caution should be exercised not to discharge a lithium-based battery too low.
Discharging a lithium-based battery below 2.5V may cut off the battery’s
protection circuit. Not all chargers accommodate a recharge on batteries that
have gone to sleep because of low voltage.
Some Li-ion batteries feature an ultra-low voltage cut-off that permanently
disconnects the pack if a cell dips below 1.5V. This precaution prohibits
recharge if a battery has dwelled in an illegal voltage state. A very deep
discharge may cause the formation of copper shunt, which can lead to a
partial or total electrical short. The same occurs if the cell is driven into
negative polarity and is kept in that state for a while. A fully discharged
battery should be charged at 0.1C. Charging a battery with a copper shunt at
the 1C rate would cause excessive heat. Such a battery should be removed
from service.
Discharging a battery too deeply is one problem; equipment that cuts off
before the energy is consumed is another. Some portable devices are not
properly tuned to harvest the optimal energy stored in a battery. Valuable
energy may be left behind if the voltage cut-off-point is set too high.
Digital devices are especially demanding on a battery. Momentary pulsed
loads cause a brief voltage drop, which may push the voltage into the cut-off
region. Batteries with high internal resistance are particularly vulnerable to
premature cut-off. If such a battery is removed from the equipment and
discharged to the appropriate cut-off point with a battery analyzer on DC load,
a high level of residual capacity can still be obtained.
Most rechargeable batteries prefer a partial rather than a full discharge.
Repeated full discharge robs the battery of its capacity. The battery chemistry
which is most affected by repeat deep discharge is lead acid. Additives to the
deep-cycle version of the lead acid battery compensate for some of the
cycling strain.
Similar to the lead acid battery, the Li-ion battery prefers shallow over
repetitive deep discharge cycles. Up to 1000 cycles can be achieved if the
battery is only partially discharged. Besides cycling, the performance of the
Li-ion is also affected by aging. Capacity loss through aging is independent of
use. However, in daily use, there is a combination of both.
The NiCd battery is least affected by repeated full discharge cycles. Several
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thousand charge/discharge cycles can be obtained with this battery system.
This is the reason why the NiCd performs well on power tools and two-way
radios that are in constant use. The NiMH is more delicate with respect to
repeated deep cycling.
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Pulse Discharge
Battery chemistries react differently to specific loading requirements.
Discharge loads range from a low and steady current used in a flashlight, to
intermittent high current bursts in a power tool, to sharp current pulses
required for digital communications equipment, to a prolonged high current
load for an electric vehicle traveling at highway speed. Because batteries are
chemical devices that must convert higher-level active materials into an
alternate state during discharge, the speed of such transaction determines the
load characteristics of a battery. Also referred to as concentration polarization,
the nickel and lithium-based batteries are superior to lead-based batteries in
reaction speed. This reflects in good load characteristics.
The lead acid battery performs best at a slow 20-hour discharge. A pulse
discharge also works well because the rest periods between the pulses help to
disperse the depleted acid concentrations back into the electrode plate. In
terms of capacity, these two discharge methods provide the highest efficiency
for this battery chemistry.
A discharge at the rated capacity of 1C yields the poorest efficiency for the
lead acid battery. The lower level of conversion, or increased polarization,
manifests itself in a momentary higher internal resistance due to the depletion
of active material in the reaction.
Different discharge methods, notably pulse discharging, also affect the
longevity of some battery chemistries. While NiCd and Li-ion are robust and
show minimal deterioration when pulse discharged, the NiMH exhibits a
reduced cycle life when powering a digital load.
In a recent study, the longevity of NiMH was observed by discharging these
batteries with analog and digital loads. In both tests, the battery discharged to
1.04V/cell. The analog discharge current was 500mA; the digital mode
simulated the load requirements of the Global System for Mobile
Communications (GSM) protocol and applied 1.65-ampere peak current for
12 ms every 100 ms. The current in between the peaks was 270mA. (Note that
the GSM pulse for voice is about 550 ms every 4.5 ms).
With the analog discharge, the NiMH wore out gradually, providing an above
average service life. At 700 cycles, the battery still provided 80 percent
capacity. By contrast, the cells faded more rapidly with a digital discharge.
The 80 percent capacity threshold was reached after only 300 cycles. This
phenomenon indicates that the kinetic characteristics for the NiMH deteriorate
more rapidly with a digital rather than an analog load.
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Discharging at High and Low
Temperature
Batteries function best at room temperature. Operating batteries at an elevated
temperature dramatically shortens their life. Although a lead acid battery may
deliver the highest capacity at temperatures above 30°C (86°F), prolonged use
under such conditions decreases the life of the battery.
Similarly, a Li-ion performs better at high temperatures. Elevated
temperatures temporarily counteracts the battery’s internal resistance, which
is a result of aging. The energy gain is short-lived because elevated
temperature promotes aging by further increasing the internal resistance.
There is one exception to running a battery at high temperature — it is the
lithium polymer with dry solid polymer electrolyte, the true ‘plastic battery’.
While the commercial Li-ion polymer uses some moist electrolyte to enhance
conductivity, the dry solid polymer version depends on heat to enable ion
flow. This requires that the battery core be kept at an operation temperature of
60°C to 100°C.
The dry solid polymer battery has found a niche market as backup power in
warm climates. The battery is kept at the operating temperature with built-in
heating elements. During normal operation, the core is kept warm with power
derived from the utility grid. Only on a power outage would the battery need
to provide power to maintain its own heat. To minimize heat loss, the battery
is insulated.
The Li-ion polymer as standby battery is said to outperform VRLA batteries
in terms of size and longevity, especially in shelters in which the temperature
cannot be controlled. The high price of the Li-ion polymer battery remains an
obstacle.
The NiMH chemistry degrades rapidly if cycled at higher ambient
temperatures. Optimum battery life and cycle count are achieved at 20°C
(68°F). Repeated charging and discharging at higher temperatures will cause
irreversible capacity loss. For example, if operated at 30°C (86°F), the cycle
life is reduced by 20 percent. At 40°C (104°F), the loss jumps to a whopping
40 percent. If charged and discharged at 45°C (113°F), the cycle life is only
half of what can be expected if used at moderate room temperature. The NiCd
is also affected by high temperature operation, but to a lesser degree.
At low temperatures, the performance of all battery chemistries drops
drastically. While -20°C (-4°F) is threshold at which the NiMH, SLA and
Li-ion battery stop functioning, the NiCd can go down to -40°C (-40°F). At
that frigid temperature, the NiCd is limited to a discharge rate of 0.2C (5 hour
rate). There are new types of Li-ion batteries that are said to operate down to
-40°C.
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It is important to remember that although a battery may be capable of
operating at cold temperatures, this does not automatically mean it can also be
charged under those conditions. The charge acceptance for most batteries at
very low temperatures is extremely confined. Most batteries need to be
brought up to temperatures above the freezing point for charging. The NiCd
can be recharged at below freezing provided the charge rate is reduced
to 0.1C.
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Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6
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Chapter 6: The Secrets of
Battery Runtime
Is the runtime of a portable device directly related to the size of the battery
and the energy it can hold? In most cases, the answer is yes. But with digital
equipment, the length of time a battery can operate is not necessarily linear to
the amount of energy stored in the battery.
In this chapter we examine why the specified runtime of a portable device
cannot always be achieved, especially after the battery has aged. We address
the four renegades that are affecting the performance of the battery. They are:
declining capacity, increasing internal resistance, elevated self-discharge, and
premature voltage cut-off on discharge.
Declining Capacity
The amount of charge a battery can hold gradually decreases due to usage,
aging and, with some chemistries, lack of maintenance. Specified to deliver
about 100 percent capacity when new, the battery eventually requires
replacement when the capacity drops to the 70 or 60 percent level. The
warranty threshold is typically 80 percent.
The energy storage of a battery can be divided into three imaginary sections
consisting of available energy, the empty zone that can be refilled and the
rock content that has become unusable. Figure 6-1 illustrates these three
sections of a battery.
In nickel-based batteries, the rock content may be in the form of crystalline
formation, also known as memory. Deep cycling can often restore the
capacity to full service. Also known as ‘exercise’, a typical cycle consists of
one or several discharges to 1V/cell with subsequent discharges.
Figure 6-1: Battery charge capacity.
Three imaginary sections of a battery
consisting of available energy, empty zone
and rock content.
With usage and age, the rock content grows.
Without regular maintenance, the user may
end up carrying rocks instead of batteries.
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The loss of charge acceptance of the Li-ion/polymer batteries is due to cell
oxidation, which occurs naturally during use and as part of aging. Li-ion
batteries cannot be restored with cycling or any other external means. The
capacity loss is permanent because the metals used in the cells are designated
to run for a specific time only and are being consumed during their
service life.
Performance degradation of the lead acid battery is often caused by sulfation,
a thin layer that forms on the negative cell plates, which inhibits current flow.
In addition, there is grid corrosion that sets in on the positive plate. With
sealed lead acid batteries, the issue of water permeation, or loss of electrolyte,
also comes into play. Sulfation can be reversed to a certain point with cycling
and/or topping charge but corrosion and permeation are permanent. Adding
water to a sealed lead acid battery may help to restore operation but the
long-term results are unpredictable.
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Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article: Memory, myth
or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article: Battery testers for
modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel Cell, Is it Ready?
> Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6
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Increasing Internal Resistance
To a large extent, the internal resistance, also known as impedance, determines
the performance and runtime of a battery. If measured with an AC signal, the
internal resistance of a battery is also referred to as impedance. High internal
resistance curtails the flow of energy from the battery to the equipment.
A battery with simulated low and high internal resistance is illustrated below.
While a battery with low internal resistance can deliver high current on demand, a
battery with high resistance collapses with heavy current. Although the battery
may hold sufficient capacity, the voltage drops to the cut-off line and the ‘low
battery’ indicator is triggered. The equipment stops functioning and the remaining
energy is undelivered.
Figure 6-2: Effects of
impedance on battery load.
A battery with low
impedance provides
unrestricted current flow and
delivers all available energy.
A battery with high
impedance cannot deliver
high-energy bursts due to a
restricted path, and
equipment may cut off
prematurely.
NiCd has the lowest internal resistance of all commercial battery systems, even
after delivering 1000 cycles. In comparison, NiMH starts with a slightly higher
resistance and the readings increase rapidly after 300 to 400 cycles.
Maintaining a battery at low internal resistance is important, especially with
digital devices that require high surge current. Lack of maintenance on
nickel-based batteries can increase the internal resistance. Readings of more than
twice the normal resistance have been observed on neglected NiCd batteries. After
applying a recondition cycle with the Cadex 7000 Series battery analyzer, the
readings on the batteries returned to normal. Reconditioning clears the cell plates
of unwanted crystalline formations, which restores proper current flow.
Li-ion offers internal resistance characteristics that are between those of NiMH
and NiCd. Usage does not contribute much to the increase in resistance, but aging
does. The typical life span of a Li-ion battery is two to three years, whether it is
used or not. Cool storage and keeping the battery in a partially charged state when
not in use retard the aging process.
The internal resistance of the Li-ion batteries cannot be improved with cycling.
The cell oxidation, which causes high resistance, is non-reversible. The ultimate
cause of failure is high internal resistance. Energy may still be present in the
battery, but it can no longer be delivered due to poor conductivity.
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With effort and patience, lead acid batteries can sometimes be improved by
cycling or applying a topping and/or equalizing charge. This reduces the
current-inhibiting sulfation layer but does not reverse grid corrosion.
Figure 6-3 compares the voltage signature and corresponding runtime of a battery
with low, medium and high internal resistance when connected to a digital load.
Similar to a soft ball that easily deforms when squeezed, the voltage of a battery
with high internal resistance modulates the supply voltage and leaves the imprint
of the load. The current pulses push the voltage towards the end-of-discharge line,
resulting in a premature cut-off.
When measuring the battery with a voltmeter after the equipment has cut off and
the load is removed, the terminal voltage commonly recovers and the voltage
reading appears normal. This is especially true of nickel-based batteries.
Measuring the open terminal voltage is an unreliable method to establish the
state-of-charge (SoC) of the battery.
A battery with high impedance may perform well if loaded with a low DC current
such as a flashlight, portable CD player or wall clock. With such a gentle load,
virtually all of the stored energy can be retrieved and the deficiency of high
impedance is masked.
Figure 6-3: Discharge curve.
This chart compares the runtime of batteries with similar capacities under low,
medium and high impedance when connected to a pulsed load.
The internal resistance of a battery can be measured with dedicated impedance
meters. Several methods are available, of which the most common are applying
DC loads and AC signals. The AC method may be done with different
frequencies. Depending on the level of capacity loss, each technique provides
slightly different readings. On a good battery, the measurements are reasonably
close; on a weak battery, the readings between the methods may disperse more
drastically.
Modern battery analyzers offer internal resistance measurements as a battery
quick-test. Such tests can identify batteries that would fail due to high internal
resistance, even though the capacity may still be acceptable. Internal battery
resistance measurements are available in the Cadex 7000 Series battery analyzers.
(See Chapter 9: Internal Battery Resistance.)
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6
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Elevated Self-Discharge
All batteries exhibit a certain amount of self-discharge; the highest is visible
on nickel-based batteries. As a rule, a nickel-based battery discharges 10 to
15 percent of its capacity in the first 24 hours after charge, followed by 10 to
15 percent every month thereafter.
The self-discharge on the Li-ion battery is lower compared to the nickel-based
systems. The Li-ion self-discharges about five percent in the first 24 hours
and one to two percent thereafter. Adding the protection circuit increases the
self-discharge to ten percent per month.
One of the best batteries in terms of self-discharge is the lead acid system; it
only self-discharges five percent per month. It should be noted, however, that
the lead acid family has also the lowest energy density among current battery
systems. This makes the system unsuitable for most hand-held applications.
At higher temperatures, the self-discharge on all battery chemistries increases.
Typically, the rate doubles with every 10°C (18°F). Large energy losses occur
through self-discharge if a battery is left in a hot vehicle. On some older
batteries, stored energy may get lost during the course of the day through
self-discharge rather than actual use.
The self-discharge of a battery increases with age and usage. For example, a
NiMH battery is good for 300 to 400 cycles, whereas a NiCd adequately
performs over 1000 cycles before high self-discharge affects the performance
of the battery. Once a battery exhibits high self-discharge, no remedy is
available to reverse the effect. Factors that accelerate self-discharge on
nickel-based batteries are damaged separators (induced by excess crystalline
formation, allowing the packs to cook while charging), and high cycle count,
which promotes swelling in the cell.
Figure 6-4: Effects of high load
impedance.
A battery may gradually
self-discharge as a result of high
temperature, high cycle count
and age. In older batteries, stored
energy may be lost during the
course of the day through
self-discharge rather than actual
use.
At present, no simple quick-test is available to measure the self-discharge of a
battery. A battery analyzer can be used by first reading the initial capacity
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after full charge, then measuring the capacity again after a rest period of
12 hours. The Cadex 7000 Series performs this task automatically. In the
future, quick test methods may be available that are able to measure the
self-discharge of a battery within a few seconds.
Premature Voltage Cut-off
Some portable equipment does not fully utilize the low-end voltage spectrum
of a battery. The equipment cuts off before the designated end-of-discharge
voltage is reached and some precious battery power remains unused.
A high cut-off voltage problem is more widespread than is commonly
assumed. For example, a certain brand of mobile phone that is powered with a
single-cell Li-ion battery cuts off at 3.3V. The Li-ion can be designed to be
used to 3V and lower. With a discharge to 3.3V, only about 70 percent of the
expected 100 percent capacity is utilized. Another mobile phone using NiMH
and NiCd batteries cuts off at 5.7V. The four-cell nickel-based batteries are
designed to discharge to 5V.
Figure 6-5: Illustration of equipment with
high cut-off voltage.
Some portable devices do not utilize all
available battery power and leave precious
energy behind.
When discharging these batteries to their respective end-of-discharge
threshold with a battery analyzer after the equipment has cut off, up to
60 percent residual capacity readings can be retrieved. High residual
capacity is prevalent with batteries that have elevated internal resistance and
are operated at warm ambient temperatures. Digital devices that load the
battery with current bursts are more receptive to premature voltage cut-off
than analog equipment.
A ’high cut-off voltage’ is mostly equipment related. In some cases the
problem of premature cut-off is induced by a battery with low voltage. A low
table voltage is often caused by a battery pack that contains a cell with an
electrical short. Memory also causes a decrease in voltage; however, this is
only present in nickel-based systems. In addition, elevated temperature lowers
the voltage level on all battery systems. Voltage reduction due to high
temperatures is temporary and normalizes once the battery cools down.
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> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7
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Chapter 7: The ‘Smart’ Battery
Aspeaker at a battery seminar remarked that, “The battery is a wild animal
and artificial intelligence domesticates it.” An ordinary or ‘dumb’ battery has
the inherit problem of not being able to display the amount of reserve energy
it holds. Neither weight, color, nor size provides any indication of the
battery’s state-of-charge (SoC) and state-of-health (SoH). The user is at the
mercy of the battery when pulling a freshly charged battery from the charger.
Help is at hand. An
increasing number of
today’s rechargeable
batteries are made
‘smart’. Equipped with a
microchip, these
batteries are able to
communicate with the
charger and user alike to
provide statistical
information. Typical applications for ‘smart’ batteries are notebook computers
and video cameras. Increasingly, these batteries are also used in advanced
biomedical devices and defense applications.
There are several types of ‘smart’ batteries, each offering different
complexities, performance and cost. The most basic ‘smart’ battery may only
contain a chip to identify its chemistry and tell the charger which charge
algorithm to apply. Other batteries claim to be smart simply because they
provide protection from overcharging, under-discharging and short-circuiting.
In the eyes of the Smart Battery System (SBS) forum, these batteries cannot
be called ‘smart’.
What then makes a battery ‘smart’? Definitions still vary among organizations
and manufacturers. The SBS forum states that a ‘smart’ battery must be able
to provide SoC indications. Benchmarq was the first company to
commercialize the concept of the battery fuel gauge technology. Early IC
chips date back to 1990. Several manufacturers followed suit and produced
‘smart’ chips for batteries.
During the early nineties, numerous ‘smart’ battery architectures with a SoC
read-out have emerged. They range from the single wire system, the two-wire
system and the system management bus (SMBus). Most two-wire systems are
based on the SMBus protocol. This book will address the single wire system
and the SMBus.
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The Single Wire Bus
The single wire system is the simpler of the two and does all the data
communications through one wire. A battery equipped with the single wire
system uses only three wires, the positive and negative battery terminals and
the data terminal. For safety reasons, most battery manufacturers run a
separate wire for temperature sensing. Figure 7-1 shows the layout of a single
wire system.
The modern single wire system stores battery-specific data and tracks battery
parameters, including temperature, voltage, current and remaining charge.
Because of simplicity and relatively low hardware cost, the single wire enjoys
a broad market acceptance for high-end mobile phones, two-way radios and
camcorders.
Most single wire systems do not have a common form factor; neither do they
lend themselves to standardized SoH measurements. This produces problems
for a universal charger concept. The Benchmarq single wire solution, for
example, cannot measure current directly; it must be extracted from a change
in capacity over time.
In addition, the single wire bus allows battery SoH measurement only when
the host is ‘married’ to a designated battery pack. Such a fixed host-battery
relationship is feasible with notebook computers, mobile phones or video
cameras, provided the appropriate OEM battery is used. Any discrepancy in
the battery type from the original will make the system unreliable or will
provide false readings.
Figure 7-1: Single wire system of
a ‘smart’ battery.
Only one wire is needed for data
communications. Rather than
supplying the clock signal from the
outside, the battery includes an
embedded clock generator. For
safety reasons, most battery
manufacturers run a separate wire
for temperature sensing.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7
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The SMBus
The SMBus is the most complete of all systems. It represents a large effort
from the portable electronic industry to standardize to one communications
protocol and one set of data. The SMBus is a two-wire interface system
through which simple power-related chips can communicate with the rest of
the system. One wire handles the data; the second is the clock. It uses I²C as
its backbone. Defined by Philips, the I²C is a synchronous multi-drop
bi-directional communications system, which operates at a speed of up to 100
kilohertz (kHz).
The Duracell/Intel SBS, in use today, was standardized in 1993. In previous
years, computer manufacturers had developed their own proprietary ‘smart’
batteries. With the new SBS specification, a broader interface standard was
made possible. This reduces the hurdles of interfering with patents and
intellectual properties.
In spite of an agreed standard, many large computer manufacturers, such as
IBM, Compaq and Toshiba, have retained their proprietary batteries. The
reason for going their own way is partly due to safety, performance and form
factor. Manufacturers claim that they cannot guarantee safe and enduring
performance if a non-brand battery is used. To make the equipment as
compact as possible, the manufacturers explain that the common form factor
battery does not optimally fit their available space. Perhaps the leading motive
for using their proprietary batteries is pricing. In the absence of competition,
these batteries can be sold for a premium price.
The early SMBus batteries had problems of poor accuracy. Electronic circuits
did not provide the necessary resolution; neither was real time reporting of
current, voltage and temperature adequate. On some batteries, the specified
accuracy could only be achieved if the battery was new, operated at room
temperature and was discharged at a steady rate of 1C. Operating in adverse
temperatures or discharging at uneven loads reduced the accuracy
dramatically. Most loads for portable equipment are uneven and fluctuate with
power demand. There are power surges on a laptop at start up and refresh,
high inrush currents on biomedical equipment during certain procedures and
sharp pulse bursts on digital communications devices on transmit.
In the absence of a reliable reporting system on the older generation of ‘smart’
batteries, capacity estimation was inaccurate. This resulted in powering down
the equipment before the battery was fully depleted, leaving precious energy
behind. Most batteries introduced in the late 1990s have resolved some or all
of these deficiencies. Further improvements will be necessary.
Design— The design philosophy behind the SMBus battery is to remove the
charge control from the charger and assign it to the battery. With a true
SMBus system, the battery becomes the master and the charger serves as a
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slave that must follow the dictates of the battery. This is done out of concerns
over charger quality, compatibility with new and old battery chemistries,
administration of the correct amount of charge currents and accurate
full-charge detection. Simplifying the charging for the user is an issue that is
important when considering that some battery packs share the same footprint
but contain radically different chemistries.
The SMBus system allows new battery chemistries to be introduced without
the charger becoming obsolete. Because the battery controls the charger, the
battery manages the voltage and current levels, as well as cut-off thresholds.
The user does not need to know which battery chemistry is being used.
The analogy of charging a ‘smart’ and ‘dumb’ battery can be made with the
eating habits of an adult and a baby. Charging a ‘smart’ battery resembles the
eating choices of a responsible adult who knows best what food to select how
much to take. The baby, in on the other hand, has limited communications
skills in expressing the type and amount of food desired. Putting this analogy
in parallel with charging batteries, the charger servicing ‘dumb’ batteries can
only observe the approximate SoC level and avoid overcharge conditions.
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Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
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Architecture — An SMBus battery contains permanent and temporary data.
The permanent data is programmed into the battery at the time of
manufacturing and include battery ID number, battery type, serial number,
manufacturer’s name and date of manufacture. The temporary data is acquired
during use and consists of cycle count, user pattern and maintenance
requirements. Some of the temporary data is being replaced and renewed
during the life of the battery.
The SMBus is divided into Level 1, 2 and 3. Level 1 has been eliminated
because it does not provide chemistry independent charging. Level 2 is
designed for in-circuit charging. A laptop that charges its battery within the
unit is a typical example of Level 2. Another application of Level 2 is a
battery that contains the charging circuit within the pack. Level 3 is reserved
for full-featured external chargers.
Most external SMBus chargers are based on Level 3. Unfortunately, this level
is complex and the chargers are costly to manufacture. Some lower cost
chargers have emerged that accommodate SMBus batteries but are not fully
SBS compliant. Manufacturers of SMBus batteries do not readily endorse this
shortcut. Safety is always a concern, but customers buy these economy
chargers because of the lower price.
Figure 7-2: Two-wire SMBus
system.
The SMBus is based on a two-wire
system using a standardized
communications protocol. This
system lends itself to standardized
state-of-charge and state-of-health
measurements.
Serious industrial battery users operating biomedical instruments, data
collection devices and survey equipment use Level 3 chargers with
full-fledged charge protocol. No shortcuts are applied. To assure
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compatibility, the charger and battery are matched and only approved packs
are used. The need to test and approve the marriage between specific battery
and charger types is unfortunate given that the ‘smart’ battery is intended to
be universal.
Among the most popular SMBus batteries for portable computers are the
35 and 202 form-factors. Manufactured by Sony, Hitachi, GP Batteries,
Moltech (formerly Energizer), Moli Energy and many others, this battery
works (should work) in all portable equipment designed for this system.
Figure 7-3 illustrates the 35 and 202 series ‘smart' batteries. Although the ‘35’
has a smaller footprint compared to the ‘202’, most chargers are designed to
accommodate all sizes, provided the common five-prong knife connector
is used.
Figure 7-3: 35 and 202 series ‘smart’ batteries featuring SMBus.
Available in NiCd, NiMH and Li-ion chemistries, these batteries are used for
mobile computing, biomedical instruments and high-end survey equipment.
The same form factor also accommodates NiCd and NiMH chemistries but
without SMBus (‘dumb’).
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
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or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
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Negatives of the SMBus — Like any good invention, the SMBus battery has
some serious downsides that must be addressed. For starters, the ‘smart’
battery costs about 25 percent more than the ‘dumb’ equivalent. In addition,
the ‘smart’ battery was intended to simplify the charger, but a full-fledged
Level 3 charger costs substantially more than a regular dumb model.
A more serious issue is maintenance requirements, better known as capacity
re-learning. This procedure is needed on a regular basis to calibrate the
battery. The Engineering Manager of Moli Energy, a large Li-ion cell
manufacturer commented, “With the Li-ion battery we have eliminated the
memory effect, but are we introducing digital memory with the SMBus
battery?”
Why is calibration needed? The answer is in correcting the tracking errors that
occur between the battery and the digital sensing circuit during use. The most
ideal battery use, as far as fuel-gauge accuracy is concerned, is a full charge
followed by a full discharge at a constant 1C rate. This ensures that the
tracking error is less than one percent per cycle. However, a battery may be
discharged for only a few minutes at a time and commonly at a lower C-rate
than 1C. Worst of all, the load may be uneven and vary drastically.
Eventually, the true capacity of the battery no longer synchronizes with the
fuel gauge and a full charge and discharge are needed to ‘re-learn’ or calibrate
the battery.
How often is calibration needed? The answer lies in the type of battery
application. For practical purposes, a calibration is recommended once every
three months or after every 40 short cycles. Long storage also contributes to
errors because the circuit cannot accurately compensate for self-discharge.
After extensive storage, a calibration cycle is recommended prior to use.
Many applications apply a full discharge as part of regular use. If this occurs
regularly, no additional calibration is needed. If a full discharge has not
occurred for a few months and the user notices the fuel gauge losing accuracy,
a deliberate full discharge on the equipment is recommended. Some
intelligent equipment advises the user when a calibrating discharge is needed.
This is done by measuring the tracking error and estimating the discrepancy
between the fuel gauge reading and that of the chemical battery.
What happens if the battery is not calibrated regularly? Can such a battery be
used in confidence? Most ‘smart’ battery chargers obey the dictates of the
cells rather than the electronic circuit. In this case, the battery will be fully
charged regardless of the fuel gauge setting. Such a battery is able to function
normally, but the digital readout will be inaccurate. If not corrected, the fuel
gauge information simply becomes a nuisance.
The level of non-compliance is another problem with the SMBus. Unlike
other tightly regulated standards, such as the long play record introduced in
the late 1950s, the audiocassette in the 1960s, the VCR in the 1970s, ISDN
and GSM in the 1980s and the USB in the 1990s, some variations are
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permitted in the SMBus protocol. These are: adding a check bid to halt the
service if the circuit crashes, counting the number of discharges to advise on
calibration and disallowing a charge if a certain fault condition has occurred.
Unfortunately, these variations cause problems with some existing chargers.
As a result, a given SMBus battery should be checked for compatibility with
the designated charger before use to assure reliable service. Ironically, the
more features that are added to the SMBus charger and battery, the higher the
likelihood of incompatibilities.
‘Smart’ battery technology has not received the widespread acceptance that
battery manufacturers had hoped. Some engineers go so far as to suggest that
the SMBus battery is a ‘misguided principal’. Design engineers may not have
fully understood the complexity of charging batteries in the incubation period
of the ‘smart’ battery. Manufacturers of SMBus chargers are left to clean up
the mess.
The forecast in consumer acceptance of the ‘smart’ battery has been too
optimistic. In the early 1990s when the SMBus battery was conceived, price
many not have been as critical an issue as it is now. Then, the design engineer
would include many wonderful options. Today, we look for scaled down
products that are economically priced and perform the function intended.
When looking at the wireless communications market, adding high-level
intelligence to the battery is simply too expensive for most consumers. In the
competitive mobile phone market, for example, the features offered by the
SMBus would be considered overkill.
SMBus battery technology is mainly used by higher-level industrial
applications and battery manufacturers are constantly searching for avenues to
achieve a wider utilization of the ‘smart’ battery. According to a survey in
Japan, about 30 percent of all mobile computing devices are equipped with a
‘smart’ battery.
Improvements in the ‘smart’ battery system, such as better compatibilities,
improved error-checking functions and higher accuracies will likely increase
the appeal of the ‘smart’ battery. Endorsement by large software
manufacturers such as Microsoft will entice PC manufacturers to make full
use of these powerful features.
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Copyright 2001 Isidor Buchmann. All rights reserved.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7
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The State-of-Charge Indicator
Most SMBus batteries are equipped with a charge level indicator. When
pressing a SoC button on a battery that is fully charged, all signal lights
illuminate. On a partially discharged battery, half the lights illuminate, and on
an empty battery, all lights remain dark. Figure 7-4 shows such a fuel gauge.
Figure 7-4: State-of-charge
readout of a ‘smart’ battery.
Although the state-of-charge is
displayed, the state-of-health and
its predicted runtime are
unknown.
While SoC information displayed on a battery or computer screen is helpful,
the fuel gauge resets to 100 percent each time the battery is recharged,
regardless of the battery’s SoH. A serious miscount occurs if an aged battery
shows 100 percent after a full-charge, when in fact the charge acceptance has
dropped to 50 percent or less. The question remains: “100 percent of what?”
A user unfamiliar with this battery has little information about the runtime of
the pack.
The Tri-State Fuel Gauge
The SoC information alone is incomplete without knowing the battery’s SoH.
To fully evaluate the present state of a battery, three levels of information are
needed. They are: SoC, SoH and the empty portion of the battery that can be
replenished with a charge. (The empty portion is derived by deducting the
SoC from the SoH.)
How can the three levels of a battery be measured and made visible to the
user? While the SoC is relatively simple to produce, as discussed above,
measuring the SoH is more complex. Here is how it works:
At time of manufacture, each SMBus battery is given its specified SoH status,
which is 100 percent by default. This information is permanently programmed
into the pack and does not change. With each charge, the battery resets to the
full-charge status. During discharge, the energy units (coulombs) are counted
and compared against the 100 percent setting. A perfect battery would
indicate 100 percent on a calibrated fuel gauge. As the battery ages and the
charge acceptance drops, the SoH begins to indicate lower readings. The
discrepancy between the factory set 100 percent and the actual delivered
coulombs is used to calculate the SoH.
Knowing the SoC and SoH, a simple linear display can be made. The SoC is
indicated with green LED’s; the empty part remains dark; and the unusable
part is shown with red LED’s. Figure 7-5 shows such a tri-state fuel gauge. As
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an alternative, the colored bar display may be replaced with a numeric display
indicating SoH and SoC.
Figure 7-5: Tri-state fuel gauge.
The Battery Health Gauge reads the ‘learned’ battery information available on
the SMBus and displays it on a multi-colored LED bar. This illustration
shows a partially discharged battery of 50% SoC with a 20% empty portion
and an unusable portion of 30%.
The most practical setting to place the tri-state-fuel gauge is on a charger.
Only one display would be needed for a multi-bay charging unit. To view the
readings of a battery, the user would simply press a button. The SoC and SoH
information would be displayed within five seconds after inserting the battery
into the charger bay. During charge, the gauge would reveal the charge level
of each battery. This information would be handy when a functional battery is
needed in a hurry. Cadex offers a series of SMBus chargers that feature the
tri-state fuel gauge as an option.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7
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The Target Capacity Selector
For users that simply need a go/no go answer and do not want to bother about
other battery information, chargers are available that feature a target capacity
selector. Adjustable to 60, 70 or 80 percent, the target capacity selector acts as
a performance check and flags batteries that do not meet set requirements.
If a battery falls below target, the charger triggers the condition light. The user
is prompted to press the condition button to cycle the battery. Condition
consists of charge/discharge/charge and performs calibration and conditioning
functions. If the battery does not recover after the conditioning service, the
fail light illuminates, indicating that the battery should be replaced. A green
ready light at the completion of the program assures that the battery meets the
required performance level.
An SMBus charger with the above described features acts as charger,
conditioner and quality control system. Figure 76 illustrates a two-bay Cadex
charger featuring the target capacity selector and discharge circuit. This unit is
based on Level 3 and services both SMBus and ‘dumb’ batteries.
Some SMBus chargers can be fully automated to apply a conditioning cycle
whenever the battery falls below the target setting. An override button cancels
the discharge if a fast-charge is needed instead. Such a system maximizes the
life of fleet batteries and assures that deadwood is identified and removed.
Figure 7-6:The Cadex SM2+ charger
This Level 3 charger serves as charger,
conditioner and quality control system.
It reads the battery’s true
state-of-health and flags those that fall
below the set target capacity. Each bay
operates independently and charges
NiCd, NiMH and Liion chemistries in
approximately three hours. ‘Dumb’
batteries can also be charged.
By allowing the user to set the desired battery performance level, the question
is raised as to what level to select. The answer is governed by the
applications, reliability standards and cost policies.
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It should be noted that the batteries are always charged to 100 percent,
regardless of the target setting. The target capacity simply refers to the
amount of charge the battery has delivered on the last discharge.
A practical target capacity setting for most applications is 80 percent.
Decreasing the threshold to 70 percent will lower the performance standard
but pass more batteries. A direct cost saving will result. The 60 percent level
may suit those users who run a low budget operation, have ready access to
replacement batteries and can live with shorter, less predictable runtimes.
Battery SoH readings are only available with Level 3 SMBus chargers
servicing valid SMBus batteries. ‘Dumb’ batteries cannot provide SoH
readings, even if they share the identical footprint of the ‘smart’ battery and
can use the same charger.
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> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
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Fuel Gauges for Large Batteries
Most ‘smart’ battery applications today are limited to portable electronic
equipment, and the electronic circuit is built right into the battery pack. In
applications where larger ‘smart’ batteries are needed, such as electric
wheelchairs, scooters, robots and forklifts, the electronic circuit may be
placed in a box external to the battery.
The main benefit of adding intelligence to the battery is to enable the
measurement of SoH and reserve energy. Most measuring devices used are
based on voltage, which is known to be highly inaccurate.
Cadex is extending the ‘smart’ battery technology to wheeled applications.
Called the Cadex Fuelcheck™, the device is based on the tri-state fuel gauge
described earlier in this section. The system consists of a controller, current
measuring device and a display unit. The Cadex Fuelcheck™ device can be
added to new equipment when it is manufactured and can be installed in
existing equipment as a retrofit. The installation is permanent and each
wheeled appliance requires one system.
A tri-state linear bar graph consisting of colored LED’s would be the
preferred display for a personal user, such as a wheelchair operator. By
replacing the light display with a digital readout, additional information can
be shown. For example, a display could indicate the remaining runtime based
on the average power consumption logged. Corrections would be applied if
the load factor changes during the course of the day. Figure 77 illustrates a
digital fuel gauge using the LCD panel.
To initialize the Cadex Fuelcheck™ system, a one-time setup procedure is
required. A PC will prompt the technician to enter information such as battery
chemistry, desired end-of-discharge voltage, Ah rating of the battery, and
designated service flags. The system is then calibrated by applying a full
charge, followed by a full discharge. The initial discharge assesses the battery,
or learns the performance. The SoH readings will be known after the first full
discharge.
7-7: Cadex Fuelcheck™ digital
fuel gauge.
The display indicates SoC, SoH,
remaining power in hours, the
voltage and current draw.
The simplest way to discharge the battery as part of calibration is to run it
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down through normal use in the equipment. The most accurate readings are
obtained by using a load bank. Such a device may not be always available.
With a data logging option built into the system, the PC allows downloading
service data that have been collected during use. Such information would
benefit large equipment fleets and rental places that need to check the
performance of the batteries on demand.
Similar to other ‘smart’ battery systems, calibration will be needed once every
6 to 12 months. More frequent calibrations may be required if the equipment
is used for short durations between each recharge. The most practical way to
calibrate the system is by occasionally allowing the battery to run down
through continued use. Information relating to the date of the last calibration,
or an early call for calibration if certain conditions occur, can be calculated
and displayed.
Knowing the SoH of a battery at any time and scheduling timely service or
replacement is a major benefit for industrial battery users. Such a system
would be especially helpful for organizations in which different individuals
use the equipment and no one is given maintenance responsibilities.
Equipment rental places fall into this category.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8
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Chapter 8: Choosing the Right
Battery
What causes a battery to wear down — is it mechanical or chemical? The
answer is ‘both’. A battery is a perishable product that starts deteriorating
from the time it leaves the factory. Similar to a spring under tension, a battery
seeks to revert to its lowest denominator. The rate of aging is subject to depth
of discharge, environmental conditions, charge methods and maintenance
procedures (or lack thereof). Each battery chemistry behaves differently in
terms of aging and wear through normal use.
What’s the best battery for mobile
phones?
When buying a replacement
battery, the buyer often has the
choice of different battery
chemistries. Li-ion and Li-ion
polymer batteries are used on
newer phones, whereas the NiMH
and NiCd are found in older
models. If the buyer has a choice,
the sales person may advise a
customer to go for the highest
capacity rating and to stay away from the NiCd because of the memory effect.
The customer may settle for the slim-line NiMH because it offers relatively
high capacity in a small package and is reasonably priced.
Seemingly a wise choice, an analysis in this chapter reveals that other
chemistries may have served better. The NiMH offers good value for the price
but falls short in expected cycle life. Although excellent when new, the
performance trails off quickly after about 300 cycles due to decreased
capacity and rising internal resistance. In comparison, the Li-ion can be used
for about 500 cycles. The best cycle count is achieved with NiCd. Properly
maintained, the NiCd delivers over 1000 cycles and the internal resistance
remains low. However, the NiCd offers about 30 percent less capacity
compared to the NiMH. In addition, the NiCd is being removed from the
mobile phone market because of environmental concerns.
Switching to environmentally friendlier batteries is fitting, especially in the
mobile phone market where the NiMH performs reasonably well and can be
economical. The battery disposal issue is difficult to control, particularly in
the hands of a diverse user group.
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The NiMH and NiCd are
considered high maintenance
batteries, which require regular
discharge cycles to prevent what
is referred to as ‘memory’.
Although the NiMH was
originally advertised as
memory-free, both NiCd and
NiMH are affected by the
phenomenon. The capacity loss is caused by crystalline formation that is
generated by the positive nickel plate, a metal shared by both systems.
Nickel-based batteries, especially NiCd’s, should be fully discharged once per
month. If such maintenance is omitted for four months or more, the capacity
drops by as much as one third. A full restoration becomes more difficult the
longer service is withheld.
It is not recommended to discharge a battery before each charge because this
wears down the battery unnecessarily and shortens the life. Neither is it
advisable to leave a battery in the charger for a long period of time. When not
in use, the battery should be put on a shelf and charged before use. Always
store the battery in a cool place.
Is the Li-ion a better choice? Yes, for many applications. The Li-ion is a low
maintenance battery which offers high energy, is lightweight and does not
require periodic full discharge. No trickle charge is applied once the battery
reaches full charge. The Li-ion battery can stay in most chargers until used.
The charging process of a Li-ion is, in many ways, simpler and cleaner than
that of nickel-based systems, but requires tighter tolerances. Repeated
insertion into the charger or cradle does not affect the battery by inducing
overcharge.
On the negative side, the Li-ion gradually loses charge acceptance as part of
aging, even if not used. For this reason, Li-ion batteries should not be stored
for long periods of time but be rotated like perishable food. The buyer should
be aware of the manufacturing date when purchasing a replacement battery.
The Li-ion is most economical for those who use a mobile phone daily. Up to
1000 charge/discharge cycles can be expected if used within the expected
service life of about two to three years. Because of the aging effect, the Li-ion
does not provide an economical solution for the occasional user. If the Li-ion
is the only battery choice and the equipment is seldom used, the battery
should be removed from the equipment and stored in a cool place, preferably
only partially charged.
So far, little is known about the life expectancy of the Li-ion polymer.
Because of the similarities with the Li-ion, the long-term performance of both
systems is expected to be similar. Much effort is being made to prolong the
service life of lithium-based systems. New chemical additives have been
effective in retarding the aging process.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8
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What’s the best battery for two-way
radios?
The two-way radio market uses mostly NiCd batteries. In the last few years,
environmental agencies have been attempting to discourage the use of NiCd,
especially in Europe. NiMH have been tried and tested in two-way radios for
a number of years but the results are mixed. Shorter cycle life compared to
NiCd is the major drawback.
The reasons for the relatively short life of NiMH are multi-fold. NiMH is less
robust than NiCd and has a cycle life expectancy that is half or one third that
of the standard NiCd. In addition, NiMH prefers a moderate discharge current
of 0.5C or less. A two-way radio, on the other hand, draws a discharge current
of about 1.5A when transmitting at 4W of power. High discharge loads
shorten the life of the NiMH battery considerably.
NiCd has the advantage of maintaining a low and steady internal resistance
throughout most of its service life. Although low when new, NiMH increases
the resistance with advanced cycle count. A battery with high internal
resistance causes the voltage to drop when a load is applied. Even though
energy may still be present, the battery cannot deliver the high current flow
required during transmit mode. This results in a drop in voltage, which
triggers the ‘low battery’ condition and the radio cuts off. This happens
mostly during transmission.
The Li-ion has been tested for use with two-way radios but has not been able
to provide the ultimate answer. Higher replacement costs, restrictions posed
by the safety circuit and aging pose limitations on this battery system.
What’s the best battery for laptops?
Batteries for laptops have a unique challenge because they must be small and
lightweight. In fact, the laptop battery should be invisible to the user and
deliver enough power to
last for a five-hour flight
from Toronto to
Vancouver. In reality, a
typical laptop battery
provides only about
90 minutes of service.
Computer manufacturers
are hesitant to add a larger
battery because of increased size and weight. A recent survey indicated that,
given the option of larger size and more weight to obtain longer runtimes,
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most users would settle for what is being offered today. For better or worse,
we have learned to accept the short runtime of a laptop.
During the last few years, batteries have improved in terms of energy density.
Any benefit in better battery performance, however, is being eaten up by the
higher power requirements of the laptops. It is predicted that the even more
power-hungry PC’s of the future will counteract any improvements in battery
technology, as marginal as they might be. The net effect will result in the
same runtimes but faster and more powerful computers.
The length of time the battery can be used will get shorter as the battery ages.
A battery residing in a laptop ages more quickly than when used in other
applications. After a warm-up, the official operating temperature inside a
laptop computer is 45°C (113°F). Such a high ambient temperature drastically
lowers the battery’s life expectation. At a temperature of 45°C, for example,
the life expectancy of a NiMH battery is less than 50 percent as compared to
running it at the ideal operating temperature of 20°C (68°F).
The Li-ion does not fare much better. At this high ambient temperature, the
wear-down effect of the battery is primarily governed by temperature as
opposed to cycle count. The situation is worsened by the fact that the battery
resides in a high SoC most of the time. The combination of heat and high SoC
promotes cell oxidation, a condition that cannot be reversed once afflicted.
A fully charged Li-ion battery that is stored at 45°C suffers a capacity loss
from 100 percent to about 70 percent in as little as six months. If this
condition persists, the capacity degrades further to 50 percent in twelve
months. In reality, the battery in a laptop is exposed to elevated temperatures
just during use and the battery is in a full charge state only part of the time.
But leaving the laptop in a parked car under the hot sun will aggravate the
situation.
Some Japanese computer manufacturers have introduced a number of
sub-notebooks in which the battery is mounted externally, forming part of the
hinge. This design improves battery life because the battery is kept at room
temperature. Some models carry several size batteries to accommodate
different user patterns.
What then is the best battery for a laptop? The choices are limited. The NiCd
has virtually disappeared from the mobile computer scene and the NiMH is
loosing steam, paving the way for the Li-ion. Eventually, very slim geometry
will also demand thin batteries, and this is possible with the prismatic Li-ion
polymer.
Besides providing reliable performance for general portable use, the Li-ion
battery also offers superior service for laptop users who must continually
switch from fixed power to battery use, as is the case for many sales people.
Many biomedical and industrial applications follow this pattern also. Here is
the reason why such use can be hard on some batteries:
On a nickel-based charging system, unless smart, the charger applies a full
charge each time the portable device is connected to fixed power. In many
cases, the battery is already fully charged and the cells go almost immediately
into overcharge. The battery heats up, only to be detected by a sluggish
thermal charge control, which finally terminates the fast charge. Permanent
capacity loss caused by overcharge and elevated temperature is the result.
Among the nickel-based batteries, NiMH is least capable of tolerating a
recharge on top of a charge. Adding elevated ambient temperatures to the
charging irregularities, a NiMH battery can be made inoperable in as little as
six months. In severe cases, the NiMH is known to last only 2 to 3 months.
For mixed battery and utility power use, the Li-ion system is a better choice.
If a fully charged Li-ion is placed on charge, no charge current is applied. The
battery only receives a recharge once the terminal voltage has dropped to a set
threshold. Neither is there a concern if the device is connected to fixed power
for long periods of time. No overcharge can occur and there is no memory to
worry about.
NiMH is the preferred choice for a user who runs the laptop mostly on fixed
power and removes the battery when not needed. This way, the battery is only
engaged if the device is used in portable mode. The NiMH battery can thus be
kept fresh while sitting on the shelf. NiMH ages well if kept cool and only
partially charged.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8
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Selecting a Lasting Battery
As part of an ongoing research program to find the optimum battery system
for selected applications, Cadex has performed life cycle tests on NiCd,
NiMH and Li-ion batteries. All tests were carried out on the Cadex 7000
Series battery analyzers in the test labs of Cadex, Vancouver, Canada. The
batteries tested received an initial full-charge, and then underwent a regime of
continued discharge/charge cycles. The internal resistance was measured with
Cadex’s Ohmtest™ method, and the self-discharge was obtained from
time-to-time by reading the capacity loss incurred during a 48-hour rest
period. The test program involved 53 commercial telecommunications
batteries of different models and chemistries. One battery of each chemistry
displaying typical behavior was chosen for the charts below.
When conducting battery tests in a laboratory, it should be noted that the
performance in a protected environment is commonly superior to those in
field use. Elements of stress and inconsistency that are present in everyday
use cannot always be simulated accurately in the lab.
The NiCd Battery — In terms of life cycling, the standard NiCd is the most
enduring battery. In Figure 8-1 we examine the capacity, internal resistance
and self-discharge of a 7.2V, 900mA NiCd battery with standard cells. Due to
time constraints, the test was terminated after 2300 cycles. During this period,
the capacity remains steady, the internal resistance stays flat at 75mW and the
self-discharge is stable. This battery receives a grade ‘A’ for almost perfect
performance.
The readings on an ultra-high capacity NiCd are less favorable but still better
than other chemistries in terms of endurance. Although up to 60 percent
higher in energy density compared to the standard NiCd version, Figure 8-2
shows the ultra-high NiCd gradually losing capacity during the 2000 cycles
delivered. At the same time, the internal resistance rises slightly. A more
serious degradation is the increase of self-discharge after 1000 cycles. This
deficiency manifests itself in shorter runtimes because the battery consumes
some energy itself, even if not in use.
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Figure 8-1: Characteristics of a standard cell NiCd battery.
This battery deserves an ‘A’ for almost perfect performance in terms of stable
capacity, internal resistance and self-discharge over many cycles. This
illustration shows results for a 7.2V, 900mA NiCd.
Figure 8-2: Characteristics of a NiCd battery with ultra-high capacity cells.
This battery is not as favorable as the standard NiCd but offers higher energy
densities and performs better than other chemistries in terms of endurance.
This illustrations shows results for a 6V, 700mA NiCd.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8
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The NiMH Battery — Figure 8-3 examines the NiMH, a battery that offers
high energy density at reasonably low cost. We observe good performance at
first but past the 300-cycle mark, the performance starts to drift downwards
rapidly. One can detect a swift increase in internal resistance and
self-discharge after cycle count 700.
Figure 8-3: Characteristics of a NiMH battery.
This battery offers good performance at first but past the 300-cycle mark, the
capacity, internal resistance and self-discharge start to deteriorate rapidly.
This illustrations shows results for a 6V, 950mA NiMH.
The Li-ion Battery — The Li-ion battery offers advantages that neither the
NiCd nor NiMH can match. In Figure 8-4 we examine the capacity and
internal resistance of a typical Li-ion. A gentle capacity drop is observed over
1000 cycles and the internal resistance increases only slightly. Because of low
readings, self-discharge was omitted for this test.
The better than expected performance of this test battery may be due to the
fact that the test did not include aging. The lab test was completed in about
200 days. A busy user may charge the battery once every 24 hours. With such
a user pattern, 500 cycles would represent close to two years of normal use
and the effects of aging would become apparent.
Manufacturers of commercial Li-ion batteries specify a cycle count of 500. At
that stage, the battery capacity would drop from 100 to 80 percent. If operated
at 40°C (104°F) rather than at room temperature, the same battery would only
deliver about 300 cycles.
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Figure 8-4: Characteristics of a Li-ion battery.
The above-average performance of this battery may be due to the fact that the
test did not include aging. This illustration shows results for a 3.6V, 500mA
Li-ion battery.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9
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Chapter 9: Internal Battery
Resistance
With the move from analog to digital devices, new demands are being placed
on the battery. Unlike analog equipment that draws a steady current, the
digital mobile phone, for example, loads the battery with short, high current
bursts.
Increasingly, mobile
communication devices are
moving from voice only to
multimedia which allows
sending and receiving data,
still pictures and even video.
Such transmissions add to
the bandwidth, which
require several times the
battery power compared to
voice only.
One of the urgent requirements of a battery for digital applications is low
internal resistance. Measured in milliohms (mW), the internal resistance is the
gatekeeper that, to a large extent, determines the runtime. The lower the
resistance, the less restriction the battery encounters in delivering the needed
power bursts. A high mW reading can trigger an early ‘low battery’ indication
on a seemingly good battery because the available energy cannot be delivered
in an appropriate manner.
Figure 9-1 examines the major global mobile phone systems and compares
peak power and peak current requirements. The systems are the AMP, GSM,
TDMA and CDMA.
AMP
GSM
TDMA1
CDMA
Type
Analog
Digital
Digital
Digital
Used in
USA, Canada Globally USA, Canada USA, Canada
Peak Power
0.6W
1-2W
0.6-1W
0.2W
Peak current2
0.3A DC
1-2.5A
0.8-1.5A
0.7A
In service since
1985
1986
1992
1995
Figure 9-1: Peak power requirements of popular global mobile phone systems.
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Moving from voice to multi-media requires several times the battery power.
1. Some TDMA handsets feature dual mode (analog 800mA DC load;
digital 1500mA pulsed load).
2. Current varies with battery voltage; a 3.6V battery requires higher
current than a 7.2V battery.
Why do seemingly good batteries fail
on digital equipment?
Service technicians have been puzzled by the seemingly unpredictable battery
behavior when powering digital equipment. With the switch from analog to
digital wireless communications devices, particularly mobile phones, a battery
that performs well on an analog device may show irrational behavior when
used on a digital device. Testing these batteries with a battery analyzer
produces normal capacity readings. Why then do some batteries fail
prematurely on digital devices but not on analog?
The overall energy requirement of a digital mobile phone is less than that of
the analog equivalent, however, the battery must be capable of delivering high
current pulses that are often several times that of the battery’s rating. Let’s
look at the battery rating as expressed in C-rates.
A 1C discharge of a battery rated at 500mAh is 500mA. In comparison, a 2C
discharge of the same battery is 1000mA. A GSM phone powered by a
500mA battery that draws 1.5A pulses loads the battery with a whopping 3C
discharge.
A 3C rate discharge is fine for a battery with very low internal resistance.
However, aging batteries, especially Li-ion and NiMH chemistries, pose a
challenge because the mW readings of these batteries increase with use.
Improved performance can be achieved by using a larger battery, also known
as an extended pack. Somewhat bulkier and heavier, an extended pack offers
a typical rating of about 1000mAh or roughly double that of the slim-line. In
terms of C-rate, the 3C discharge is reduced to 1.5C when using a 1000mAh
instead of a 500mAh battery.
As part of ongoing research to find the best battery system for wireless
devices, Cadex has performed life cycle tests on various battery systems. In
Figure 9-2, Figure 9-3, and Figure 9-4, we examine NiCd, NiMH and Li-ion
batteries, each of which generates a good capacity reading when tested with a
battery analyzer but produce stunning differences on a pulsed discharge of
1C, 2C and 3C. These pulses simulate a GSM phone.
Figure 9-2: Talk-time of a NiCd battery under the GSM load schedule.
This battery has 113% capacity and 155m© internal resistance.
A closer look reveals vast discrepancies in the m© measurements of the test
batteries. In fact, these readings are typical of batteries that have been in use
for a while. The NiCd shows 155mW, the NiMH 778mW and the Li-ion
320mW, although the capacities checked in at 113, 107 and 94 percent
respectively when tested with the DC load of a battery analyzer. It should be
noted that the internal resistance was low when the batteries were new.
Figure 9-3: Talk-time of a NiMH battery under the GSM load schedule.
This battery has 107% capacity and 778m© internal resistance.
Figure 9-4: Talk-time of a Li-ion battery under the GSM load schedule.
This battery has 94% capacity and 320m© internal resistance.
From these charts we can see that the talk-time is in direct relationship with
the battery’s internal resistance. The NiCd performs best and produces a talk
time of 140 minutes at 1C and a long 120 minutes at 3C. In comparison, the
NiMH is good for 140 minutes at 1C but fails at 3C. The Li-ion provides
105 minutes at 1C and 50 minutes at 3C discharge.
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Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article: Memory, myth
or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article: Battery testers for
modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel Cell, Is it Ready?
> Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9
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How is the internal battery resistance
measured?
A number of techniques are used to measure internal battery resistance. One
common method is the DC load test, which applies a discharge current to the
battery while measuring the voltage drop. Voltage over current provides the
internal resistance (see Figure 9-5).
Figure 9-5: DC load test.
The DC load test measures the battery’s internal resistance by reading the voltage
drop. A large drop indicates high resistance.
The AC method, also known as the conductivity test, measures the
electrochemical characteristics of a battery. This technique applies an alternating
current to the battery terminals. Depending on manufacturer and battery type, the
frequency ranges from 10 to 1000Hz. The impedance level affects the phase shift
between voltage and current, which reveals the condition of the battery. The AC
method works best on single cells. Figure 9-6 demonstrates a typical phase shift
between voltage and current when testing a battery.
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Figure 9-6: AC load test.
The AC method measures the phase shift between voltage and current. The
battery’s reactance is used to calculate the impedance.
Some AC resistance meters evaluate only the load factor and disregard the phase
shift information. This technique is similar to the DC method. The AC voltage
that is superimposed on the battery’s DC voltage acts as brief charge and
discharge pulses. The amplitude of the ripple is utilized to calculate the internal
battery resistance.
Cadex uses the discreet DC method to measure internal battery resistance. Added
to the Cadex 7000 Series battery analyzers, a number of charge and discharge
pulses are applied, which are scaled to the mAh rating of the battery tested. Based
on the voltage deflections, the battery’s internal resistance is calculated. Known as
Ohmtest™, the mW reading is obtained in five seconds. Figure 9-7 shows the
technique used.
Figure 9-7: Cadex Ohmtest™.
Cadex’s pulse method measures the voltage deflections by applying charge and
discharge pulses. Higher deflections indicate higher internal resistance.
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> Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance or hype? >
Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article:
Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article:
Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The
Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 >
Chapter 9
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Figure 9-8 compares the three methods of measuring the internal resistance of a
battery and observe the accuracy. In a good battery, the discrepancies between
methods are minimal. The test results deviate to a larger degree on packs with
poor SoH.
Impedance measurement alone does not provide a definite conclusion as to the
battery performance. The mW readings may vary widely and are dependent on
battery chemistry, cell size (mAh rating), type of cell, number of cells connected
in series, wiring and contact type.
Figure 9-8: Comparison of the AC, DC and Cadex Ohmtest™ methods.
State-of-health readings were obtained using the Cadex 7000 Series battery
analyzer by applying a full charge/discharge/charge cycle. The DC method on
the 68% SoH battery exceeded 1000mW.
When using the impedance method, a battery with a known performance should
be measured and its readings used as a reference. For best results, a reference
reading should be on hand for each battery type. Figure 9-9kl; provides a
guideline for digital mobile phone batteries based on impedance readings.
The milliohm readings are related to the battery voltage. Higher voltage batteries
allow higher internal resistance because less current is required to deliver the
same power. The ratio between voltage and milliohm is not totally linear. There
are certain housekeeping components that are always present whether the battery
has one or several cells. These are wiring, contacts and protection circuits.
Temperature also affects the internal resistance of a battery. The internal
resistance of a naked Li-ion cell, for example, measures 50mW at 25°C (77°F).
If the temperature increases, the internal resistance decreases. At 40°C (104°F),
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the internal resistance drops to about 43mW and at 60°C (140°F) to 40mW.
While the battery performs better when exposed to heat, prolonged exposure to
elevated temperatures is harmful. Most batteries deliver a momentary
performance boost when heated.
Milli-Ohm
Battery Voltage
Ranking
75-150mOhm
3.6V
Excellent
150-250mOhm
3.6V
Good
250-350mOhm
3.6V
Marginal
350-500mOhm
3.6V
Poor
Above 500mOhm
3.6V
Fail
Figure 9-9: Battery state-of-health based on internal resistance.
The milliohm readings relate to the battery voltage; higher voltage allows higher
milliohm readings.
Cold temperatures have a drastic effect on all batteries. At 0°C (32°F), the
internal resistance of the same Li-ion cell drops to 70mW. The resistance
increases to 80mW at -10°C (50°F) and 100mW at -20°C (-4°F).
The impedance readings work best with Li-ion batteries because the
performance degradation follows a linear pattern with cell oxidation. The
performance of NiMH batteries can also be measured with the impedance
method but the readings are less dependable. There are instances when a poorly
performing NiMH battery can also exhibit a low mW reading.
Testing a NiCd on resistance alone is unpredictable. A low resistance reading
does not automatically constitute a good battery. Elevated impedance readings
are often caused by memory, a phenomenon that is reversible. Internal resistance
values have been reduced by a factor of two and three after servicing the affected
batteries with the recondition cycle of a Cadex 7000 Series battery analyzer. Of
cause, high internal resistance can have sources other than memory alone.
What’s the difference between internal
resistance and impedance?
The terms ‘internal resistance’ and ‘impedance’ are often intermixed when
addressing the electrical conductivity of a battery. The differences are as
follows: The internal resistance views the conductor from a purely resistive
value, or ohmic resistance. A comparison can be made with a heating element
that produces warmth by the friction of electric current passing through.
Most electrical loads are not purely resistive, rather, they have an element of
reactance. If an alternating current (AC) is sent through a coil, for example, an
inductance (magnetic field) is created, which opposes current flow. This AC
impedance is always higher than the ohmic resistance of the copper wire. The
higher the frequency, the higher the inductive resistance becomes. In
comparison, sending a direct current (DC) through a coil constitutes an electrical
short because there is only a very small ohmic resistance.
Similarly, a capacitor does not allow the flow of DC, but passes AC. In fact, a
capacitor is an insulator for DC. The resistance that is present when sending an
AC current flowing through a capacitor is called capacitance. The higher the
frequency, the lower the capacitive resistance.
A battery as a power source combines ohmic, inductive and capacitive
resistance. Figure 9-10 represents these resistive values on a schematic diagram.
Each battery type exhibits slightly different resistive values.
Figure 9-10: Ohmic, inductive and capacitive resistance in batteries.
● Ro = ohmic resistance
●
Qc = constant phase loop (type of capacitance)
●
●
L = inductor
Zw = Warburg impedance (particle movement within the electrolyte)
●
Rt = transfer resistance
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10
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Chapter 10: Getting the Most
from your Batteries
A common difficulty with portable equipment is the gradual decline in battery
performance after the first year of service. Although fully charged, the battery
eventually regresses to a point where the available energy is less than half of
its original capacity, resulting in unexpected downtime.
Downtime almost always occurs at
critical moments. This is especially
true in the public safety sector
where portable equipment runs as
part of a fleet operation and the
battery is charged in a pool setting,
often with minimal care and
attention. Under normal
conditions, the battery will hold
enough power to last the day.
During heavy activities and longer
than expected duties, a marginal battery cannot provide the extra power
needed and the equipment fails.
Rechargeable batteries are known to cause more concern, grief and frustration
than any other part of a portable device. Given its relatively short life span,
the battery is the most expensive and least reliable component of a portable
device.
In many ways, a rechargeable battery exhibits human-like characteristics: it
needs good nutrition, it prefers moderate room temperature and, in the case of
the nickel-based system, requires regular exercise to prevent the phenomenon
called ‘memory’. Each battery seems to develop a unique personality of
its own.
Memory: myth or fact?
The word ‘memory’ was
originally derived from
‘cyclic memory’, meaning
that a NiCd battery can
remember how much
discharge was required on
previous discharges.
Improvements in battery
technology have virtually
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eliminated this phenomenon.
Tests performed at a Black
& Decker lab, for example,
showed that the effects of cyclic memory on the modern NiCd were so small
that they could only be detected with sensitive instruments. After the same
battery was discharged for different lengths of time, the cyclic memory
phenomenon could no longer be noticed.
The problem with the nickel-based battery is not the cyclic memory but the
effects of crystalline formation. There are other factors involved that cause
degeneration of a battery. For clarity and simplicity, we use the word
‘memory’ to address capacity loss on nickel-based batteries that are
reversible.
The active cadmium material of a NiCd battery is present in finely divided
crystals. In a good cell, these crystals remain small, obtaining maximum
surface area. When the memory phenomenon occurs, the crystals grow and
drastically reduce the surface area. The result is a voltage depression, which
leads to a loss of capacity. In advanced stages, the sharp edges of the crystals
may grow through the separator, causing high self-discharge or an electrical
short.
Another form of memory that occurs on some NiCd cells is the formation of
an inter-metallic compound of nickel and cadmium, which ties up some of the
needed cadmium and creates extra resistance in the cell. Reconditioning by
deep discharge helps to break up this compound and reverses the
capacity loss.
The memory phenomenon can be explained in layman’s terms as expressed
by Duracell: “The voltage drop occurs because only a portion of the active
materials in the cells is discharged and recharged during shallow or partial
discharging. The active materials that have not been cycled change in physical
characteristics and increase in resistance. Subsequent full discharge/charge
cycling will restore the active materials to their original state.”
When NiMH was first introduced there was much publicity about its
memory-free status. Today, it is known that this chemistry also suffers from
memory but to a lesser extent than the NiCd. The positive nickel plate, a
metal that is shared by both chemistries, is responsible for the crystalline
formation.
New NiCd cell.
The anode is in fresh condition (capacity
of 8.1Ah). Hexagonal cadmium hydroxide
crystals are about 1 micron in cross
section, exposing large surface area to the
liquid electrolyte for maximum
performance.
Cell with crystalline formation.
Crystals have grown to an enormous 50 to
100 microns in cross section, concealing
large portions of the active material from
the electrolyte (capacity of 6.5Ah). Jagged
edges and sharp corners may pierce the
separator, which can lead to increased
self-discharge or electrical short.
Restored cell.
After pulsed charge, the crystals are
reduced to 3 to 5 microns, an almost 100%
restoration (capacity of 8.0A). Exercise or
recondition are needed if the pulse charge
alone is not effective.
Figure 10-1: Crystalline formation on NiCd cell.
Illustration courtesy of the US Army Electronics Command in Fort
Monmouth, NJ, USA.
In addition to the crystal-forming activity on the positive plate, the NiCd also
develops crystals on the negative cadmium plate. Because both plates are
affected by crystalline formation, the NiCd requires more frequent discharge
cycles than the NiMH. This is a non-scientific explanation of why the NiCd is
more prone to memory than the NiMH.
The stages of crystalline formation of a NiCd battery are illustrated in
Figure 10-1. The enlargements show the negative cadmium plate in normal
crystal structure of a new cell, crystalline formation after use (or abuse) and
restoration.
Lithium and lead-based batteries are not affected by memory, but these
chemistries have their own peculiarities. Current inhibiting pacifier layers
affect both batteries — plate oxidation on the lithium and sulfation and
corrosion on the lead acid systems. These degenerative effects are
non-correctible on the lithium-based system and only partially reversible on
the lead acid.
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Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article: Memory, myth
or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article: Battery testers for
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> Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9 > Chapter 10
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How to Restore and Prolong
Nickel-based Batteries
The effects of crystalline formation are most pronounced if a nickel-based battery
is left in the charger for days, or if repeatedly recharged without a periodic full
discharge. Since most applications do not use up all energy before recharge, a
periodic discharge to 1V/cell (known as exercise) is essential to prevent the
buildup of crystalline formation on the cell plates. This maintenance is most
critical for the NiCd battery.
All NiCd batteries in regular use and on standby mode (sitting in a charger for
operational readiness) should be exercised once per month. Between these
monthly exercise cycles, no further service is needed. The battery can be used
with any desired user pattern without the concern of memory.
The NiMH battery is affected by memory also, but to a lesser degree. No
scientific research is available that compares NiMH with NiCd in terms of
memory degradation. Neither is information on hand that suggests the optimal
amount of maintenance required to obtain maximum battery life. Applying a full
discharge once every three months appears right. Because of the NiMH battery’s
shorter cycle life, over-exercising is not recommended.
A hand towel must be cleaned periodically. However, if it were washed after each
use, its fabric would wear out very quickly. In the same way, it is neither
necessary nor advisable to discharge a rechargeable battery before each charge —
excessive cycling puts extra strain on the battery.
Exercise and Recondition — Research has shown that if no exercise is applied to
a NiCd for three months or more, the crystals ingrain themselves, making them
more difficult to break up. In such a case, exercise is no longer effective in
restoring a battery and reconditioning is required. Recondition is a slow, deep
discharge that removes the remaining battery energy by draining the cells to a
voltage threshold below 1V/cell.
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Figure 10-2: Exercising and reconditioning batteries on a Cadex battery analyzer.
This illustration shows the battery voltage during a normal discharge to 1V,
followed by the secondary discharge (recondition). Recondition consists of a
discharge to 1V/cell at a 1C load current, followed by a secondary discharge to
0.4V at a much reduced current. NiCd batteries affected by memory often restore
themselves to full service.
Tests performed by the US Army have shown that a NiCd cell needs to be
discharged to at least 0.6V to effectively break up the more resistant crystalline
formation. During recondition, the current must be kept low to prevent cell
reversal. Figure 10-2 illustrates the battery voltage during normal discharge to
1V/cell followed by the secondary discharge (recondition).
Figure 10-3 illustrates the effects of exercise and recondition. Four batteries
afflicted with various degrees of memory are serviced. The batteries are first fully
charged, then discharged to 1V/cell. The resulting capacities are plotted on a scale
of 0 to 120 percent in the first column. Additional discharge/charge cycles are
applied and the battery capacities are plotted in the subsequent columns. The solid
black line represents exercise, (discharge to 1V/cell) and the dotted line
recondition (secondary discharge at reduced current to 0.4V/cell). On this test, the
exercise and recondition cycles are applied manually at the discretion of the
research technician.
Figure 10-3: Effects of exercise and recondition.
Battery A improved capacity on exercise alone; batteries B and C required
recondition. A new battery with excellent readings improved further with
recondition.
Battery A responded well to exercise alone and no recondition was required. This
result is typical of a battery that has been in service for only a few months or has
received periodic exercise cycles. Batteries B and C, on the other hand, required
recondition (dotted line) to restore their performance. Without the recondition
function, these two batteries would need to be replaced.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10
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After service, the restored batteries were returned to full use. When examined
after six months of field use, no noticeable degradation in the restored
performance was visible. The regained capacity was permanent with no
evidence of falling back to the previous state. Obviously, the batteries would
need to be serviced on a regular basis to maintain the performance.
Applying the recondition cycle on a new battery (top line on chart) resulted in
a slight capacity increase. This capacity gain is not fully understood, other
than to assume that the battery improved by additional formatting. Another
explanation is the presence of early memory. Since new batteries are stored
with some charge, the self-discharge that occurs during storage contributes to
a certain amount of crystalline formation. Exercising and reconditioning
reverse this effect. This is why the manufacturers recommend storing
rechargeable batteries at about 40 percent charge.
The importance of exercising and reconditioning NiCd batteries is
emphasized further by a study carried out by GTE Government Systems in
Virginia, USA, for the US Navy. To determine the percentage of batteries
needing replacement within the first year of use, one group of batteries
received charge only, another group was exercised and a third group received
recondition. The batteries studied were used for two-way radios on the aircraft
carriers USS Eisenhower with 1500 batteries and USS George Washington
with 600 batteries, and the destroyer USS Ponce with 500 batteries.
With charge only (charge-and-use), the annual percentage of battery failure on
the USS Eisenhower was 45 percent (see Figure 10-4). When applying
exercise, the failure rate was reduced to 15 percent. By far the best results
were achieved with recondition. The failure rate dropped to 5 percent.
Identical results were attained from the USS George Washington and the USS
Ponce.
Maintenance Method
Annual Percentage of Batteries
Requiring Replacement
Charge only (charge-and-use)
45%
Exercise only (discharge to 1V/cell)
15%
Reconditioning (secondary deep
discharge)
5%
Figure 10-4: Replacement rates of NiCd batteries.
The annual percentage of NiCd batteries requiring replacement when used
without any maintenance decreases with exercise and recondition. These
statistics were drawn from batteries used by the US Navy on the USS
Eisenhower, USS George Washington and USS Ponce.
The GTE Government System report concluded that a battery analyzer
featuring exercise and recondition functions costing $2,500US would pay for
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itself in less than one month on battery savings alone. The report did not
address the benefits of increased system reliability, an issue that is of equal if
not greater importance, especially when the safety of human lives is at stake.
Another study involving NiCd batteries for defense applications was
performed by the Dutch Army. This involved battery packs that had been in
service for 2 to 3 years during the Balkan War. The Dutch Army was aware
that the batteries were used under the worst possible conditions. Rather than a
good daily workout, the packs were used for patrol duties lasting 2 to 3 hours
per day. The rest of the time the batteries remained in the chargers for
operational readiness.
After the war, the batteries were sent to the Dutch Military Headquarters and
were tested with Cadex 7000 Series battery analyzers. The test technician
found that the capacity of some packs had dropped to as low as 30 percent.
With the recondition function, 90 percent of the batteries restored themselves
to full field use. The Dutch Army set the target capacity threshold for field
acceptability to 80 percent. This setting is the pass/fail acceptance level for
their batteries.
Based on the successful reconditioning results, the Dutch Army now assigns
the battery maintenance duty to individual battalions. The program calls for a
service once every two months. Under this regime, the Army reports reduced
battery failure and prolonged service life. The performance of each battery is
known at any time and any under-performing battery is removed before it
causes a problem.
NiCd batteries remain the preferred chemistry for mobile communications,
both in civil and defense applications. The main reason for its continued use is
dependable and enduring service under difficult conditions. Other chemistries
have been tested and found problematic in long-term use.
During the later part of the 1990s, the US Army switched from mainly
non-rechargeable to the NiMH battery. The choice of chemistry was based on
the benefit of higher energy densities as compared to NiCd. The army soon
discovered that the NiMH did not live up to the expected cycle life. Their
reasoning, however, is that the 100 cycles attained from a NiMH pack is still
more economical than using a non-rechargeable equivalent. The army’s focus
is now on the Li-ion Polymer, a system that is more predictable than NiMH
and requires little or no maintenance. The aging issue will likely cause some
logistic concerns, especially if long-term storage is required.
Simple Guidelines
Do not leave a nickel-based battery in a charger for more than a day after full
charge is reached.
● Apply a monthly full discharge cycle. Running the battery down in the
equipment may do this also.
● Do not discharge the battery before each recharge. This would put
undue stress on the battery.
● Avoid elevated temperature. A charger should only raise the battery
temperature for a short time at full charge, and then the battery should
cool off.
● Use quality chargers to charge batteries.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10
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The Effect of Zapping
To maximize battery performance, remote control (RC) racing enthusiasts
have experimented with all imaginable methods available. One technique that
seems to work is zapping the cells with a very high pulse current. Zapping is
said to increase the cell voltage slightly, generating more power.
Typically, the racecar motor draws 30A, delivered by a 7.2V battery. This
calculates to over 200W of power. The battery must endure a race lasting
about four minutes.
According to experts, zapping works best with NiCd cells. NiMH cells have
been tried but they have shown inconsistent results.
Companies specializing in zapping NiCd for RC racing use a very high
quality Japanese NiCd cell. The cells are normally sub-C in size and are
handpicked at the factory for the application. Specially labeled, the cells are
delivered in a discharged state. When measuring the cell in empty
state-of-charge (SoC), the voltage typically reads between 1.11 to 1.12V. If
the voltage drops lower than 1.06V, the cell is considered suspect and zapping
does not seem to enhance the performance as well as on the others.
The zapping is done with a 47,000mF capacitor that is charged to 90V. Best
results are achieved if the battery is cycled twice after treatment, then is
zapped again. After the battery has been in service for a while, zapping no
longer seems to improve the cell’s performance. Neither does zapping
regenerate a cell that has become weak.
The voltage increase on a properly zapped battery is between 20 and 40mV.
This improvement is measured under a load of 30A. According to experts, the
voltage gain is permanent but there is a small drop with usage and age.
There are no apparent side effects in zapping, however, the battery
manufacturers remain silent about this treatment. No scientific explanations
are available why the method of zapping improves battery performance. There
is little information available regarding the longevity of the cells after they
have been zapped.
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How to Restore and Prolong Sealed
Lead Acid Batteries
The sealed version of the lead acid battery is designed with a low over-voltage
potential to prevent water depletion. Consequently, the SLA and VRLA
systems never get fully charged and some sulfation will develop over time.
Finding the ideal charge voltage limit for the sealed lead acid system is
critical. Any voltage level is a compromise. A high voltage limit produces
good battery performance, but shortens the service life due to grid corrosion
on the positive plate. The corrosion is permanent and cannot be reversed. A
low voltage preserves the electrolyte and allows charging under a wide
temperature range, but is subject to sulfation on the negative plate. (In
keeping with portability, this book focuses on portable SLA batteries. Due to
similarities between the SLA and VRLA systems, references to the VRLA are
made where applicable).
Once the SLA battery has lost capacity due to sulfation, regaining its
performance is often difficult and time consuming. The metabolism of the
SLA battery is slow and cannot be hurried.
A subtle indication on whether an SLA battery can be recovered is reflected in
the behavior of its discharge voltage. A fully charged SLA battery that starts
its discharge with a high voltage and tapers off gradually can be reactivated
more successfully than one on which the voltage drops rapidly when the load
is applied.
Reasonably good results in regaining lost capacity are achieved by applying a
charge on top of a charge. This is done by fully charging an SLA battery, then
removing it for a 24 to 48 hour rest period and applying a charge again. This
is repeated several times, then the capacity of the battery is checked with a
full discharge. The SLA is able to accept some overcharge, however, too long
an overcharge could harm the battery due to corrosion and loss of electrolyte.
The effect of sulfation of the plastic SLA can be reversed by applying an
over-voltage charge of up to 2.50V/cell for one to two hours. During that
time, the battery must be kept cool and careful observation is necessary.
Extreme caution is required not to raise the cell pressure to venting point.
Most plastic SLA batteries vent at 34 kPa (5 psi). Cell venting causes the
membrane on some SLA to rupture permanently. Not only do the escaping
gases deplete the electrolyte, they are also highly flammable!
The VRLA uses a cell self-regulating venting system that opens and closes
the cells based on cell pressure. Changes in atmospheric pressure contribute to
cell venting. Proper ventilation of the battery room is essential to prevent the
accumulation of hydrogen gas.
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Cylindrical SLA — The cylindrical SLA (made by Hawker) resembles an
enlarged D sized cell. After long storage, the Hawker cell can be reactivated
relatively easily. If affected by sulfation, the cell voltage under charge may
initially raise up to 5V, absorbing only a small amount of current. Within
about two hours, the small charging current converts the large sulfate crystals
back into active material. The internal cell resistance decreases and the charge
voltage eventually returns to normal. At a voltage between 2.10V and 2.40V,
the cell is able to accept a normal charge. To prevent damage, caution must be
exercised to limit the charge current.
The Hawker cells are known to regain full performance with the described
voltage method, leaving few adverse effects. This, however, does not give
credence to store this cell at a very low voltage. It is always best to follow the
manufacturer’s recommended specifications.
Improving the capacity of an older SLA by cycling is mostly unsuccessful.
Such a battery may simply be worn out. Cycling would just wear down the
battery further. Unlike nickel-based batteries, the lead acid battery is not
affected by memory.
SLA batteries are commonly rated at a 20-hour discharge. Even at such a slow
rate, a capacity of 100 percent is difficult to obtain. For practical reasons,
most battery analyzers use a 5-hour discharge when servicing SLA batteries.
This typically produces 80 to 90 percent of the rated capacity. SLA batteries
are normally overrated and manufacturers are aware of this.
Caution: When charging an SLA with over-voltage, current limiting must be
applied to protect the battery. Always set the current limit to the lowest
practical setting and observe the battery voltage and temperature during
charge. Prevent cell venting.
Important: In case of rupture, leaking electrolyte or any other cause of
exposure to the electrolyte, flush with water immediately. If eye exposure
occurs, flush with water for 15 minutes and consult a physician immediately.
Simple Guidelines
● Always keep the SLA charged. Never store below 2.10V/cell.
● Avoid repeated deep discharges. Charge more often.
● If repeated deep discharges cannot be avoided, use a larger battery to
ease the strain.
● Prevent sulfation and grid corrosion by choosing the correct charge and
float voltages.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10
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How to Prolong Lithium-based
Batteries
Today’s battery research is heavily focused on lithium chemistries, so much
so that one could assume that all future batteries will be lithium systems.
Lithium-based batteries offer many advantages over nickel and lead-based
systems. Although maintenance free, no external service is known that can
restore the battery’s performance once degraded.
In many respects, Li-ion
provides a superior service to
other chemistries, but its
performance is limited to a
defined lifespan. The Li-ion
battery has a time clock that
starts ticking as soon as the
battery leaves the factory.
The electrolyte slowly ‘eats
up’ the positive plate and the
electrolyte decays. This chemical change causes the internal resistance to
increase. In time, the cell resistance raises to a point where the battery can no
longer deliver the energy, although it may still be retained in the battery.
Equipment requiring high current bursts is affected most by the increase of
internal resistance.
Battery wear-down on lithium-based batteries is caused by two activities:
actual usage or cycling, and aging. The wear-down effects by usage and aging
apply to all batteries but this is more pronounced on lithium-based systems.
The Li-ion batteries prefer a shallow discharge. Partial discharges produce
less wear than a full discharge and the capacity loss per cycle is reduced. A
periodic full discharge is not required because the lithium-based battery has
no memory. A full cycle constitutes a discharge to 3V/cell. When specifying
the number of cycles a lithium-based battery can endure, manufacturers
commonly use an 80 percent depth of discharge. This method resembles a
reasonably accurate field simulation. It also achieves a higher cycle count
than doing full discharges.
In addition to cycling, the
battery ages even if not used.
The amount of permanent
capacity loss the battery suffers
during storage is governed by
the SoC and temperature. For
best results, keep the battery
cool. In addition, store the
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battery at a 40 percent charge level. Never fully charge or discharge the
battery before storage. The 40 percent charge assures a stable condition even
if self-discharge robs some of the battery’s energy. Most battery
manufacturers store Li-ion batteries at 15°C (59°F) and at 40 percent charge.
Simple Guidelines
● Charge the Li-ion often, except before a long storage. Avoid repeated
deep discharges.
● Keep the Li-ion battery cool. Prevent storage in a hot car. Never freeze
a battery.
● If your laptop is capable of running without a battery and fixed power is
used most of the time, remove the battery and store it in a cool place.
● Avoid purchasing spare Li-ion batteries for later use. Observe
manufacturing date when purchasing. Do not buy old stock, even if sold
at clearance prices.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10
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Battery Recovery Rate
The battery recovery rate by applying controlled discharge/charge cycles
varies with chemistry type, cycle count, maintenance practices and age of the
battery. The best results are achieved with NiCd. Typically 50 to 70 percent of
discarded NiCd batteries can be restored
when using the exercise and recondition
methods of a Cadex battery analyzer or
equivalent device.
Not all batteries respond equally well to
exercise and recondition services. An older
battery may show low and inconsistent
capacity readings with each cycle. Another will get worse when additional
cycles are applied. An analogy can be made to a very old man for whom
exercise is harmful. Such conditions indicate instabilities caused by aging,
suggesting that this pack should be replaced. In fact, some users of the Cadex
analyzers use the recondition cycle as the acid test. If the battery gets worse,
there is strong evidence that this battery would not perform well in the field.
Applying the acid test exposes the weak packs, which can no longer hide
behind their stronger peers.
Some older NiCd batteries recover to near original capacity when serviced.
Caution should be applied when ‘rehiring’ these old-timers because they may
exhibit high self-discharge. If in doubt, a self-discharge test should be
carried out.
The recovery rate of the NiMH is about 40 percent. This lower yield is, in
part, due to the NiMH’s reduced cycle count as compared to the NiCd. Some
batteries may be afflicted by heat damage that occurs during incorrect
charging. This deficiency cannot be corrected. Permanent loss of battery
capacity is also caused by prolonged
storage at elevated temperatures.
The recovery rate for lead acid
batteries is a low 15 percent. Unlike
nickel-based batteries, the restoration
of the SLA is not based on reversing
crystalline formation, but rather by
reactivating the chemical process.
The reasons for low capacity readings are prolonged storage at low terminal
voltage, and poor charging methods. The battery also fails due to age and high
cycle count.
Lithium-based batteries have a defined age limit. Once the anticipated cycles
have been delivered, no method exists to improve the battery. The main
reason for failure is high internal resistance caused by oxidation. Operating
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the battery at elevated temperatures will momentarily reduce this condition.
When the temperature normalizes, the condition of high internal resistance
returns.
The speed of oxidation depends on the storage temperature and the battery’s
charge state. Keeping the battery in a cool place can prolong its life. The
Li-ion battery should be stored at 40 percent rather than full-charge state.
An increasing number of modern batteries fall prey to the cut-off problem
induced by a deep discharge. This is especially evident on Li-ion batteries
for mobile phones. If discharged below 2.5V/cell, the internal protection
circuit often opens. Many chargers cannot apply a recharge and the battery
appears to be dead.
Some battery analyzers feature a boost, or wake-up function, to activate the
protection circuit and enable a recharge if discharged too low. If the cell
voltage has fallen too low (1.5V/cell and lower) and has remained in that state
for a few days, a recharge should not be attempted because of safety concerns
on the cell(s).
It is often asked whether a restored battery will work as good as a new one.
The breakdown of the crystalline formation can be considered a full
restoration. However, the crystalline formation will re-occur with time if the
battery is denied the
required maintenance.
When the defective
component of a machine
is replaced, only the
replaced part is new; the
rest of the machine
remains in the same
condition. If the separator of a nickel-based battery is damaged by excess heat
or is marred by uncontrolled crystalline formation, that part of the battery will
not improve.
Other methods, which claim to restore and prolong rechargeable batteries,
have produced disappointing results. One method is attaching a strong magnet
on the side of the battery; another is exposing the battery to ultrasound
vibrations. No scientific evidence exists that such methods will improve
battery performance, or restore an ailing battery.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11
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Chapter 11: Maintaining Fleet
Batteries
Unlike individual battery users, who come to know their batteries like a good
friend, fleet users must share the batteries from a pool of unknown packs.
While an individual user can detect even a slight reduction in runtime, fleet
operators have no way of knowing the behavior or condition of the battery
when pulling it from the charger. They are at the mercy of the battery. It’s
almost like playing roulette.
It is recommended that fleet
battery users set up a battery
maintenance program. Such a
plan exercises all batteries on
a regular basis, reconditions
those that fall below a set
target capacity and ‘weeds
out’ the deadwood. Usually,
batteries get serviced only
when they no longer hold a charge or when the equipment is sent in for repair.
As a result, battery-operated equipment becomes unreliable and
battery-related failures often occur. The loss of adequate battery power is as
detrimental as any other malfunction in the system.
Implementing a battery maintenance plan requires an effort by management to
schedule the required service for the battery packs. This should become an
integral component of an organization’s overall equipment maintenance and
repair activities. A properly managed program improves battery performance,
enhances reliability and cuts replacement costs.
The maintenance plan should include all rechargeable batteries in use. Large
organizations often employ a variety of batteries ranging from wireless
communications, to mobile computing, to emergency medical equipment, to
video cameras, portable lighting and power tools. The performance of these
batteries is critical and there is little room for failure.
Whether the batteries are serviced in-house with their own battery analyzers
or sent to an independent firm specializing in that service, sufficient spare
batteries are required to replace those packs that have been temporarily
removed. When the service is done on location and the batteries can be
reinstated within 24 hours, only five spares in a fleet of 100 batteries are
required. This calculation is based on servicing five batteries per day in a
20 workday month, which equals100 batteries per month. If the batteries are
sent away, five spares are needed for each day the batteries are away. If
100 batteries are absent for one week, for example, 35 spare batteries are
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needed.
Manufacturers of portable equipment support battery maintenance programs.
Not only does such a plan reduce unexpected downtime, a well-performing
battery fleet makes the equipment work better. If the recurring problems
relating to the battery can be eliminated, less equipment is sent to the service
centers. A well-managed battery maintenance program also prolongs battery
life, a benefit that looks good for the vendor.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery invented?
> Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance or hype? >
Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article:
Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article:
Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel
Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9 >
Chapter 10 > Chapter 11
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The ‘Green Light’ Lies
When charging a battery, the ready light will eventually illuminate, indicating
that the battery is fully charged. The user assumes that the battery has reached its
full potential and the battery is taken in confidence.
In no way does the ‘green light’ guarantee sufficient battery capacity or assure
good state-of-health (SoH). Similar to a toaster that pops up the bread when
brown (or black), the charger fills the battery with energy and ‘pops’ it to ready
when full (or warm).
The rechargeable battery is a corrosive device that gradually loses its ability to
hold a charge. Many users in an organization are unaware that their fleet batteries
barely last a day with no reserve energy to spare. In fact, weak batteries can hide
comfortably because little demand is placed on them in a routine day. The
situation changes when full performance is required during an emergency. Total
collapse of portable systems is common and such breakdowns are frequently
related to poor battery performance. Figure 11-1 shows five batteries in various
states of degradation.
Figure 11-1: Progressive loss of charge acceptance.
The rechargeable battery is a corrosive device that gradually loses its ability to
hold charge as part of natural aging, incorrect use and/or lack of maintenance.
The unusable part of the battery that creeps in is referred to as ‘rock content’.
Carrying larger packs or switching to higher energy-dense chemistries does not
assure better reliability if the weak batteries are not ‘weeded’ out at the
appropriate time. Likewise, the benefit of using ultra-advanced battery systems
offers little advantage if packs are allowed to remain in the fleet once their
performance has dropped below an acceptable performance level.
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Figure 11-2 illustrates four batteries with different ratings and SoH conditions.
Batteries B, C and D show reduced performance because of memory problems
and other deficiencies. The worst pack is Battery D. Because of its low charge
acceptance, this battery might switch to ready after only 14 minutes of charge
(assumed time). Ironically, this battery is a likely candidate to be picked when a
fresh battery is required in a hurry. Unfortunately, it will last only for a brief
moment. Battery A, on the other hand, has the highest capacity and takes the
longest to charge. Because the ready light is not yet lit, this battery is least likely
picked.
Figure 11-2: Comparison of charge and discharge times.
This illustration shows typical charge and discharge times for batteries with
different ratings and SoH conditions. Carrying larger batteries or switching to
high energy-dense chemistries does not necessarily assure longer runtime if
deadwood is allowed to remain in the battery fleet.
The weak batteries are charged
quicker and remain on ‘ready’
longer than the strong ones. The
bad batteries tend to gravitate to
the top. They become a target for
the unsuspecting user. In an
emergency situation that demands
quick charge action, the batteries
that show ready may simply be
those that are deadwood.
A weak battery can be compared to a fuel tank with an indentation. Refueling this
tank is quicker than a normal tank because it holds less fuel. Similar to the ‘green
light’ on a charger, the fuel gauge in the vehicle will show full when filled to the
brim, but the distance traveled before refueling will be short.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11
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Battery Maintenance, a Function of
Quality Control
The reliability of portable equipment relies almost entirely on the
performance of the battery. A dependable battery fleet can only be assured if
batteries are maintained on a periodic basis.
Battery maintenance also needs proper documentation. One simple method is
attaching a color dot, each color indicating the month of service. A different
color dot is applied when the battery is re-serviced the following month. A
numbering system indicating the month of service also works well.
A better system is attaching a full battery label containing service date and
capacity. Like the pending service on a car, the label shows the user when
maintenance is due. For critical missions, the user will pick a battery with the
highest capacity and the most recent service date. The label ensures a properly
serviced replacement pack.
Battery analyzers are available that print a label revealing the organization,
group, service date, expiry date (time to service the battery), battery capacity
and ID number. The label is generated automatically when the battery is
removed from the analyzer. Figure 11-3 illustrates such a label.
11-3: Sample battery label.
The battery label keeps track of the battery
in the same way a service sticker on a car
reminds the owner of pending service.
The battery labeling system is simple to manage. It is self-governing in the
sense that the users would only pick a battery that is properly labeled and has
recently been serviced. The system does not permit batteries to fall though the
cracks and be forgotten. It is in the interest of the user to ensure continued
reliability by bringing in batteries with dated labels for service.
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Battery Maintenance Made Simple
Several methods are available to maintain a fleet of batteries. A simple,
self-governing system is illustrated in Figure 11-4 to Figure 11-6. Only
30 minutes per day should be required for a technician to maintain the system.
One or several battery analyzers are needed that are capable of producing
battery labels.
Figure 11-4: Sorting batteries for servicing.
Each time a battery is taken from the charger, the user checks the service date
on the label attached to the battery. If the date has expired, the battery is
placed in a box marked ‘To be serviced’.
Figure 11-5: Servicing expired batteries.
Batteries with expired dates are exercised; those that do not recover to the
preset target capacity are reconditioned. Batteries that pass are re-certified by
attaching a new label with dates and capacity reading.
Figure 11-6: Returning batteries to circulation.
After servicing, the restored batteries are returned to the charger; those that
failed are replaced with new ones. Battery maintenance assures that all packs
perform at the expected capacity level.
When taking a battery from the charger, the user checks the service date on
the battery label. If expired, the battery is placed into the box marked: ‘To be
serviced’. Periodically, the box is removed and the batteries are serviced and
re-certified with a battery analyzer.
After service, the batteries are re-labeled and returned to the charger. Those
batteries that fail to meet the target capacity are replaced with new packs. All
batteries in the charger are now certified to meet a required performance
standard.
Battery maintenance has been simplified with the introduction of battery
analyzers that offer a target capacity selection. All batteries must meet a
user-defined performance test or target capacity to pass. Nickel-based
batteries that fall short of the required capacity are automatically restored with
the analyzer’s recondition cycle. Those packs that fail to recover are
subsequently replaced with new packs.
Recondition is only effective for nickel-based batteries. It is worth noting that
batteries with high self-discharge and/or shorted cells cannot be corrected
with recondition; neither can a battery be restored that is worn out or has been
damaged through abuse.
Another group of batteries that cannot be deep discharged by recondition are
‘smart’ batteries. This includes any pack that contains a microchip that must
be maintained by a continuous voltage supply. Discharging these batteries
below a certain voltage point will put the battery to sleep. A recharge often
fails to wake up these batteries.
Battery Maintenance as a Business
Some entrepreneurs have come up with the novel idea of providing a service
to test and restore rechargeable batteries. They operate in convenient locations
such as downtown cores, shopping malls and transportation hubs. Customers
bring in their batteries to have them serviced. The packs are tested and
reconditioned with automated battery analyzers. A full performance report is
issued with each battery serviced, showing service date, performance status
and the date for the next service. The suggested fee per battery is $10.00US.
Higher prices can be requested on specialty batteries which are expensive to
replace.
For organizations using a large number of batteries, a special pick-up and
delivery service can be organized to provide scheduled maintenance. This
ensures that fleet batteries used by organizations are regularly maintained.
Such a service would benefit firms that do not want to bother with battery
maintenance or do not have the expertise or resources to perform the task
in-house.
Increasingly, dealers who sell mobile phones, laptops and camcorders also
provide battery service. This activity increases traffic and helps foster good
customer relations. A new battery is sold if the old one does not recover when
serviced. By knowing that a battery can be checked and possibly restored,
customers may try to salvage their weak batteries before investing in new
ones. Some dealers may be reluctant to restore used batteries for fear of
reduced battery sales.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12
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Chapter 12: Battery
Maintenance Equipment
With the increasing
volume of batteries in
circulation, battery
manufacturing is
outpacing the supply
of suitable equipment
to test these packs.
This void is especially
apparent in the mobile
phone market where
large quantities of
batteries are being
replaced under warranty without checking or attempting to restore them. The
dealers are simply not equipped to handle the influx of returned batteries,
neither is the staff trained to perform this task on a customer service level.
Testing and conditioning these batteries is a complex procedure that lies
outside the capabilities of most customer service clerks.
With the move to maintenance-free batteries and the need to test larger
numbers of batteries, the function of battery test equipment is changing.
Lengthy cycling is giving way to quick testing, improved battery preparation
and better customer service. This shift in priority is especially apparent in the
rapidly growing consumer market. In this chapter we examine modern battery
analyzers and how they adapt to the changing needs of battery service.
Conditioning Chargers
Charging batteries is often not enough, especially when it comes to
nickel-based chemistries. Periodic maintenance is needed to optimize battery
life. Some innovative manufacturers offer chargers with conditioning features.
The most basic charger models feature one or several bays with discharge
opportunity. More advanced chargers include a display to reveal the capacity.
Some chargers offer pulse charge methods. This is done to improve charge
efficiency and reduce the memory phenomenon on nickel-based batteries.
Optimal charge performance is achieved by using a pulse charge that
intersperses discharge pulses between charge pulses. Commonly referred to as
‘burp’ or ‘reverse load’ charge, this charge method promotes high surface
area on the electrodes and helps in the recombination of the gases generated
during charge.
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Some manufacturers claim that the pulse charge method conditions and
restores NiCd batteries and makes the periodic discharges redundant.
Research carried out by the US Army has revealed that pulse charging does
reduce the crystalline formation on the NiCd battery. If properly administered,
batteries charged with these pulse chargers prolong service life. For batteries
with advanced memory, however, the pulse charge method alone is not
sufficient and a full discharge or recondition cycle is needed to break down
the more stubborn crystalline formation.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12
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Battery Analyzers
There are two types of battery analyzers: the fixed current units and the
programmable devices. While fixed current units are less expensive and
generally simpler to operate, programmable analyzers are more accurate and
faster. Programmable units can better adapt to different battery needs and are
more effective in restoring weak batteries. One of the main advantages of the
programmable battery analyzer is the ability to test the batteries against preset
parameters.
Fixed current analyzers perform well in organizations that use medium size
batteries ranging from 600mAh to 1500mAh. If smaller or larger batteries are
serviced, the charge and discharge currents are compromised and the program
time is prolonged. Here is the reason why.
A fixed current battery analyzer with a current of 600mA, for example,
services a 600mAh battery in about three hours, roughly one hour for each
cycle starting with charge, followed by discharge and a final charge. Servicing
an 1800mAh battery would take three times as long. On the low end of the
scale, a problem may arise if a 400mAh battery is serviced. This battery may
not be capable of accepting a charge rate higher than 1C and the battery could
be damaged.
When purchasing a battery analyzer, there is a tendency to buy according to
price. With the need to service a larger volume of batteries of a wider variety,
second-generation buyers find the advanced features on upscale models worth
the extra cost. These features manifest themselves in reduced operator time,
increased, throughput, simpler operation and the use of less trained staff.
Adaptation to new battery systems is also made easier. Figure 12-1 illustrates
an advanced battery analyzer.
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Figure 12-1: Cadex 7400 battery analyzer
The Cadex 7400 services NiCd, NiMH, SLA and Li-ion/polymer batteries and
is programmable to a wide range of voltage and current settings. Custom
battery adapters simplify the interface with different battery types. A quick
test program measures battery state-of-health in three minutes, independent of
charge. Nickel-based batteries are automatically restored if the capacity falls
below the user-defined target capacity.
An advanced battery analyzer evaluates the condition of a battery and
implements the appropriate service to restore the battery’s performance. On
nickel-based systems, a recondition cycle is applied automatically if a
user-selected capacity level cannot be reached.
Battery chemistry, voltage and current ratings are user-programmable. These
parameters are stored in interchangeable battery adapters and configure the
analyzer to the correct function when the adapter is installed. In the Cadex
7000 Series battery analyzers, for example, each adapter is preprogrammed
with up to ten distinct configuration codes (C-codes) to enable service for all
batteries with the same footprint.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12
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Battery-specific adapters are available for all major batteries;
user-programmable cables with alligator clips accommodate batteries for
which no adapter is on hand. Batteries with shorted, mismatched or soft cells
are identified in minutes and their deficiencies are displayed on the LCD
panel.
User-selectable programs address different battery needs. The Cadex 7000
Series features ‘Prime’ to prepare a new battery for field use and ‘Auto’ to test
and recondition weak batteries from the field. ‘Custom’ allows the setting of
unique cycle sequences composed of charge, discharge, recondition, trickle
charge or any combination, including rest periods and repeats.
More and more battery analyzers now measure the internal battery resistance,
a feature that enables one to test a battery in a few seconds. The resistance
check works best with lithium-based batteries because the level of internal
cell resistance is in direct reflection to the performance. The resistance
measurements can also be used for NiMH batteries but the readings do not
fully disclose the battery’s condition.
One of the most powerful features offered in modern battery analyzers is
battery quick testing. Within two to five minutes, reasonably accurate
state-of-health (SoH) readings are available. The test is independent of the
state-of-charge (SoC). Some charge is needed, however, to facilitate the test.
New requirements of battery analyzers are the ultra-fast charge and quick
prime features. When a battery is inserted, the analyzer evaluates the battery,
applies an ultra-fast charge if needed, and prepares the battery for service
within minutes. Such a feature helps the mobile phone industry, which
receives a large number of batteries under warranty. With the proper
equipment, many of these presumably faulty batteries can be jump-started
instead of replaced.
To accurately test batteries that power digital equipment, a modern battery
analyzer is capable of discharging a battery under a simulated digital load.
The GSM waveform, for example, transmits voice data in 567 ms bursts with
currents of 1.5A and higher. By simulating these pulses, the performance of a
battery can be tested under these field conditions. Not all analyzers are
capable of simulating such short current bursts. Instead, medium-priced
battery analyzers use a slower motion to accommodate the load signals. Pulse
duration of 5 ms, or ten times slower than the true GSM, is commonly used.
Another application involving uneven load demand is the so-called
5-5-90 program used to simulate the runtime of analog two-way radios. The
battery is loaded 5 percent of the time on transmit, 5 percent on receive and
90 percent on standby. Other combinations are 10-10-80. Each stage can be
programmed to the appropriate discharge current. Because of the different
load conditions, calculating the predicted runtime in the absence of a battery
analyzer would be difficult.
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Easy operation is an important feature of any battery analyzer. This quality is
appreciated because the user is confronted with an ever-increasing number of
battery types. Displaying the battery capacity in percentage of the nominal
capacity rather than in milliampere-hours (mAh) is preferred by many users.
With the percentage readout, the user does not need to memorize the ratings
of each battery tested because this battery information is stored in the system.
The percentage readout allows an added level of automation by implementing
a recondition cycle if the set target capacity level cannot be reached.
Some analyzers are capable of setting the appropriate battery parameters
automatically when a battery is inserted. An intelligent battery adapter reads a
passive code that is imbedded in most batteries. The code may consist of a
jumper, resistor or specified thermistor value. Some battery packs contain a
memory chip that holds a digital code. On recognition of the battery, the
adapter assigns the correct service parameters. Automatic battery
identification minimizes training and allows battery service by untrained staff.
Most analyzers are capable of printing service reports and battery labels. This
feature simplifies the task of keeping track of batteries. Marking batteries with
the service date reminds the user when a battery is due for service. Labeling
works well because the basic service history is attached right to the battery.
A battery analyzer should be automated and require minimal operator time.
The task of the operator should be limited to scheduling incoming batteries
for testing, marking the batteries after service, and replacing those that did not
meet the performance criteria. Occasional selection of the correct current
rating and chemistry may also be necessary. Properly used, a battery analyzer
generates major cost savings in terms of longer battery life and more
dependable service.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12
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Battery Analyzers for
Maintenance-Free Batteries
In the past, the purpose of battery analyzers was to restore NiCd batteries
affected by ‘memory’. With today’s nickel-free batteries, memory is no
longer a problem and the modern battery analyzer assumes duties other than
conditioning weak batteries. In an environment with nickel-free batteries, the
purpose of an analyzer is shifting to performance verification, quality control,
quick testing and quick priming.
Common sense
suggests that a new
battery should always
perform flawlessly.
Yet even brand new
batteries do not always
meet manufacturer's
specifications. With a
battery analyzer, all
incoming batteries can be checked as part of a quality control procedure and a
warranty claim can be made if the capacity drops below the specified level
toward the end of the warranty period.
The typical life of a Li-ion battery is 300 to 500 discharge/charge cycles or
two to three years from the time of manufacturing. The loss of battery
capacity occurs gradually and often without the knowledge of the user. The
function of the battery analyzer is to identify weak batteries and “weed’ them
out before they become a problem.
A battery analyzer can also trouble-shoot the cause of short runtimes. There
are several reasons for this common deficiency. In some cases, the battery
may not be properly formatted when first put in service; or the original
charger does not provide a full charge. In other cases, the portable device
draws more current than specified. Many of today’s battery analyzers can
simulate the load signature of a digital device and verify the runtime
according to the load requirements.
Lithium-based batteries are sensitive to aging. If stored fully charged and at
elevated temperatures, this battery chemistry deteriorates to a 50 percent
performance level in about one year. Similar performance degradation can be
seen on NiMH batteries when used under these conditions. Although still
considered new, the user will likely blame the equipment rather than the
battery for its poor performance. The analyzer can isolate this problem.
Before adding new batteries to the battery fleet, a battery analyzer can be used
to perform a spot check to ensure proper operation. If a battery shows low
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performance due to aging, the inventory practices may be changed to the ‘just
in time’ method. Storage facilities with improved temperature control may
also be sought.
An important new function of a battery analyzer is the ability to quick test
batteries. No longer is it necessary to guess a battery’s condition by reading
the terminal voltage, measuring the internal resistance or in enrolling lengthy
charge and discharge cycles to determine its performance. Modern quick test
programs using artificial intelligence are amazingly accurate and work
independently of SoC.
Battery quick testing is finding a ready market niche with mobile phone
dealers. This feature saves money because batteries returned under warranty
can be tested. Replacements are only issued if a genuine problem is found.
Once battery quick testing has been further refined, this technology will also
find applications in the fields of biomedical, broadcast, aviation and defense.
Battery Throughput
The quantity of batteries which an analyzer is capable of servicing depends on
the number of battery bays available. The type of service programs and the
conditions of the batteries serviced also play a role. Li-ion and lead acid
batteries take longer to charge than nickel-based packs. Analyzers with fixed
charge and discharge currents require added time, especially for larger
batteries.
The four-station Cadex
7400 battery analyzer is
capable of processing four
nickel-based batteries every
4 to 8 hours on a full-service
program. Based on two
batches per day (morning
and evening attendance) and
20 working days per month,
one such analyzer can
service 160 batteries every month. The throughput of batteries with ratings
higher than 2000mA or those that need to be charged and discharged at lower
C-rates will take longer. To allow extra analyzer capacity, including
reconditioning of old batteries, one four-station analyzer is recommended for
a fleet of 100 batteries.
When first servicing a fleet of batteries with a battery analyzer, extra runtime
will be required, especially if a large number of batteries need to be restored
with the recondition cycle. Once the user-defined target capacity has been
reached, maintaining that level from then on will be easier and take less time.
When first installing a battery maintenance program, some older packs will
likely need replacing because not all batteries recover with exercise and
recondition programs.
Quick test methods require the least amount of time. The Cadex Quicktest™
available on the Cadex 7000 Series takes three minutes per battery. The time
is prolonged if a brief charge or discharge is needed prior to testing. A charge
or discharge is applied automatically if the battery resides outside the SoC
requirements of 20 to 90 percent. Unlike the maintenance program, the Cadex
Quicktest™ does not improve the battery’s performance; it simply measures
its SoH.
The Ohmtest™measurement of the Cadex 7000 Series analyzer takes ten
seconds to complete. Large numbers of batteries can be examined if the packs
are charged prior to the test. Measuring the internal battery resistance works
reasonably well if reference readings are on hand. However, there are
batteries that measure good internal resistance but do not perform well. This is
especially common with nickel-based chemistries.
There are a number of factors which affect the accuracy of the internal
resistance readings, one of which is SoC and the settling time allowed
immediately after a recharge. A newly charged battery exhibits higher
resistance readings compared to one that has rested for a while. The increased
interfacial resistance present after charging causes this. Allow the battery to
rest for one hour or more before measurement. Temperature and the number
of cells connected in series also affects the readings. Many batteries contain a
protection circuit that distorts the readings further.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery invented? >
Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance or hype? >
Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article:
Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article:
Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel
Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9 >
Chapter 10 > Chapter 11 > Chapter 12
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Battery Maintenance Software
Organizations servicing portable equipment need simplified battery testing. The
difficulty of testing batteries is brought on by the proliferation of batteries, both in
volume and diversity of models. With most standalone battery test equipment,
servicing batteries with conventional methods is complex and time consuming.
This task will only get more difficult as new battery models are added, almost
weekly. New chemistries are being introduced which have different service
requirements.
Manufacturers of battery test equipment are responding by introducing software
packages that run on a PC. Many new systems enable operating the battery
analyzers through a PC. Such products bring battery maintenance within reach of
the untrained operator.
Cadex Batteryshop™ is a system that integrates with the Cadex 7000 Series
battery analyzers. Although the analyzers are stand-alone units that can think on
their own, the software overrides the analyzer to adjust the settings, and stores the
test results obtained from the batteries. Figure 12-2 illustrates such a battery
maintenance system.
Figure 12-2: Components of a battery maintenance system.
Cadex Batteryshop™ stores the battery test results on the database. Point and
click technology programs the analyzer by selecting the battery from a listing of
over 2000 commercial batteries. The system accommodates up to 120 analyzers
for simultaneous service of 480 batteries.
Here are examples of how a computer-assisted battery testing system can simplify
operation. To service a battery with Cadex Batteryshop™, for example, the user
selects the battery model from the database, clicks the mouse, and the analyzer is
automatically configured to the correct battery parameters. Programming the
analyzer by scanning the bar code identifying the battery’s model number is also
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possible.
In the near future, the operator will be able to view a picture of the battery on a
PC monitor. Clicking on the image will reveal the various models available in
that battery family. Clicking on the correct model will program the analyzer.
For battery fleet operators, keeping track of a large battery fleet can be difficult,
especially when observing the periodic maintenance requirements. With systems
such as Cadex Batteryshop™, the battery test results can be stored in the
database. This feature enables the operator to retain battery records from birth to
retirement. Here is how this is done:
Each battery is marked with a permanent bar code label containing a unique
battery ID number. When servicing the battery, the user scans the battery ID and
the analyzer is automatically configured through the PC. All battery test results
are stored and updated in the database under the assigned battery ID number. Any
reference to this battery in terms of performance, maintenance history and even
vendor information is available with a click of a mouse.
Delivering batteries with consistent high quality is a concern for all battery
manufacturers and distributors. With advanced battery maintenance systems,
battery batches can be tested and documented to satisfy quality control standards.
Voltage, current and temperature information can be displayed in real-time
graphics.
Cadex Batteryshop™, includes specialty programs that may not be available on
other software products. For example, the program allows discharging a battery
under a given pulsed current to simulate digital load requirements. Other
programs include life cycling to evaluate the battery’s longevity, self-discharge
tests, quick formatting and priming. The Internet allows updating the battery
database to include new entries, fetching battery matrix settings for quick testing,
sending battery test results to a central location, and downloading of new
firmware for the Cadex 7000 Series battery analyzers.
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Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13
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Chapter 13: Making Battery
Quick-Test Feasible
When Sanyo, one of the largest battery manufacturers in the world, was
asked, “Is it feasible to quick test batteries?” the engineer replied decisively,
“No”. He based his conclusion on the difficulty of using a universal test
formula that applies to all battery applications, — from wireless
communications to mobile computing, and from power tools to forklifts and
electric vehicles.
Several universities, research organizations and private companies, including
Cadex, are striving to find a workable solution to battery quick testing. Many
methods have been tried, and an equal number have failed because they were
inaccurate, inconsistent and impractical.
When studying the characteristics relating to battery state-of-health and
state-of-charge (SoH and SoC, respectively) some interesting effects can be
observed. Unfortunately, these properties are cumbersome and non-linear, and
worst of all, the parameters are unique for every battery type. This inherent
complexity makes it difficult, if not impossible, to create a formula that works
for all batteries.
In spite of these seemingly insurmountable odds, battery quick testing is
possible. But the question is asked, “how accurate will it be, and how well
will it adapt to continuously changing battery chemistries?” The cost of a
commercial quick tester and the ease-of-use are other issues of concern.
Battery Specific Quick Testing
The secret of battery quick testing lies, to a large extent, in understanding how
the battery is being loaded. Battery loads vary from short current bursts for a
mobile phone using the GSM protocol, to long and fluctuating loads on
laptops, and to intermittent heavy loads for power tools.
Because of these differences in loads, a battery for a digital mobile phone
should be tested primarily for low impedance to assure a clean delivery of the
current bursts, whereas a battery for a notebook should be examined mainly
for the bulk in energy reserve. Ultra-low impedance is of less importance
here. A battery for a power tool, on the other hand, needs both — low
impedance and good power reserve.
Some quick testers simulate the equipment load and observe the voltage
signature of the battery under these conditions. The readings are compared
with the reference settings, which are stored in the tester. The resulting
discrepancies are calculated against the anticipated or ideal settings and
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displayed as the SoH readings.
The first step in obtaining quick test readings is measuring the battery’s
internal resistance, often referred to as impedance. Internal resistance
measurements take only a few seconds to complete and provide a reasonably
accurate indication of the battery’s condition, especially if a reference reading
from a good battery is available for comparison.
Unfortunately, the impedance measurement alone provides only a rough
sketch of the battery’s performance. The readings are affected by various
battery conditions, which cannot always be controlled. For example, a fully
charged battery that has just been removed from the charger shows a higher
impedance reading than one that has rested for a few hours after charge. The
elevated impedance is due to the increased interfacial resistance present after
charging. Allowing the battery to rest for an hour or two will normalize the
battery. Temperature also affects the readings. In addition, the chemistry, the
number of cells connected in series and the rating of a battery influence the
results. Many batteries also contain a protection circuit that further distorts the
readings.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery invented? >
Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance or hype? > Article:
Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article: Memory, myth
or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article: Battery testers for
modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel Cell, Is it Ready?
> Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9 > Chapter 10 >
Chapter 11 > Chapter 12 > Chapter 13
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Three-Point Quick Test
The three-point quick test uses internal battery impedance as a basis and adds the
battery voltage under charge and discharge to the equation. The readings are
evaluated and compared with reference settings stored in the tester. Let’s explore
each of these fundamentals closer to see what it entails:
Internal resistance — To measure the impedance, a battery must be at least
50 percent charged. An empty or nearly empty battery exhibits a high internal
resistance. As the battery reaches 50 percent SoH, the resistance drops, then
increases again towards full discharge or full charge. Figure 13-1 shows the
typical internal resistance curve of a NiMH as a function of charge. Note the
decrease of impedance after the battery has rested for a while. To obtain accurate
results, allow the battery to rest after discharge and charge.
Figure 13-1: Internal resistance in a NiMH battery.
Note the higher readings immediately after a full discharge and full charge. To
obtain accurate results, allow the battery to rest after discharge and charge.
Charge Voltage — During charge, the voltage of a battery must follow a narrow
predetermined path relating to time. Anomalies such as too high and too low
voltages are identified. For example, a fast initial rise reveals that the battery may
be fully charged. If the voltage overshoots, the battery may be ‘soft’. This
condition often arises when one or more cells have developed dry spots. A frozen
battery exhibits a similar effect. If, on the other hand, the voltage does not
increase in the allotted time and remains constant, an electrical short is suspected.
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Discharge Voltage — When applying a discharge, the voltage drops slightly, and
then stabilizes for most of the period in which the energy is drawn. As the battery
reaches the end-of-discharge point, the voltage drops rapidly. Observing the initial
voltage drop and measuring the voltage delta during the flat part of the discharge
curve provides some information as to the SoC. However, each battery type
behaves differently and an accurate prediction is not easy. NiCd batteries that
have a long flat voltage during most of the discharge period are more difficult to
predict using this method than chemistries which exhibit a steady voltage drop
under load.
Unfortunately, the battery’s SoC affects the three-point quick test. Even within a
charge range of 50 to 90 percent, fluctuations in the test results cannot be avoided.
Internal resistance readings further influence the final outcome. If used as a linear
correlation with capacity, internal resistance measurements can be highly
unreliable, especially with NiCd and NiMH batteries. Figure 13-2 compares the
accuracy of six batteries when tested with the three-point quick test. To establish
the true capacity, each battery was analyzed by applying a full
charge/discharge/charge cycle.
Often referred to as the ‘Feel Good Battery Tester’ because of overly optimistic
readings, the three-point quick test method fails to provide the accuracy and
repeatability that serious battery users demand.
Figure 13-2: Comparison of battery quick test methods.
Six batteries with different state-of-health conditions were quick tested. The dark
gray bars reflect the true state-of-health obtained with the Cadex 7000 Series
battery analyzer by applying a full charge/discharge/ charge cycle; the light gray
bars are readings derived using the Three-Point Quick Test.
The impression of casual battery users that this method is “better than nothing”
will not stand up to the requirements of critical industries such as biomedical, law
enforcement, emergency response, aviation and defense. Because of relatively low
cost, the three-point tester finds a strong niche in the consumer market where a
wrong reading is simply a nuisance and does not threaten human safety.
Satisfactory readings are achieved in the mobile phone market where batteries are
similar in format. It should be noted that the three-point quick test method
provides better results than merely measuring the battery’s internal resistance or
voltage.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13
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The Evolving Battery
The Li-ion battery has not yet matured. Chemical compositions change as
often as once every six months. According to Moli Energy, a large
manufacturer of Li-ion batteries, the chemical composition of Li-based
batteries changes every six months. New chemicals are discovered that
provide better load characteristics, higher capacities and longer storage life.
Although beneficial to consumers, these improvements wreak havoc with
battery testing equipment that base quick test algorithms on fixed parameters.
Why do these changes in battery composition affect the results of a quick
tester?
The early Li-ion
batteries, notably
the coke-based
variety, exhibited a
gradual drop of
voltage during
discharge. With
newer
graphite-based Li-ion batteries, flatter voltage signatures are achieved. Such
batteries provide a more stable voltage during most of the discharge cycle.
The rapid voltage drop only occurs towards the end of discharge.
A ‘hardwired’ tester looks for an anticipated voltage drop and estimates the
SoH according to fixed references. If the voltage-drop changes due to
improved battery technology, erroneous readings will result.
Diverse metals used in the positive electrode also alter the open terminal
voltage. Manganese, also referred to as spinel, has a slightly higher terminal
voltage compared to the more traditional cobalt. In addition, spinel ages
differently from cobalt. Although both cobalt and spinel systems belong to the
Li-ion family, differences in readings can be expected when the batteries are
quick tested side-by-side.
The Li-ion polymer has a dissimilar composition to the Li-ion and responds in
a different way when tested. Instruments capable of checking Li-ion batteries
may not provide reliable readings when quick testing Li-ion polymer
batteries.
The Cadex Quicktest™ Method
A battery quick text must be capable of adapting to new chemical
combinations as introduced from time to time. Cadex solves this by using a
self-learning fuzzy logic algorithm. Used to measure analog variances in an
assortment of applications, fuzzy logic is known to the industry as a universal
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approximator. Along with unique learning capabilities, this system can adapt
to new trends. Similar to a student adapting to the complexity of a curriculum,
the system learns with each battery tested. The more batteries that are
serviced, the higher the accuracy becomes.
Cadex Quicktest™ is built on the new Cadex 7000 Series battery analyzer
platform. This system features interchangeable battery adapters that contain
the battery configuration codes (C-codes). When installed, the adapter sets the
analyzer to the correct battery parameters (chemistry, voltage rating, etc.).
To enable quick testing, the battery adapters must also contain the matrix
settings for the serviced battery. While matrices for the most common
batteries are included when acquiring the adapter, the user is asked to enter
the information on those adapters that have not yet been prepared for quick
testing. This can be done in the field by ‘scanning’ the working battery.
The ‘Learn’ program of the Cadex 7000 Series battery analyzer performs this
task by applying charge-discharge-charge activities on the test battery. Similar
to downloading a program into a PC, the information derived from the battery
sets the matrices and prepares the Cadex Quicktest™ function. The ‘Learn’
program completes its cycle within approximately four hours. One learning
cycle is the minimal requirement to enable the Cadex Quicktest™ function.
With only one battery learned or scanned, the confidence level is ‘marginal’.
Running additional batteries through the learning program will fill the matrix
registers and the confidence level will increase to ‘good’ or ‘excellent’. Like a
bridge that needs several pillars for proper support, the most accurate quick
test results are achieved by scanning individual batteries that have SoH
readings of around 100, 80 and 60 percent. The confidence level attained for a
given battery adapter is indicated on the LCD panel of the analyzer.
The Cadex Quicktest™ can be performed with charge levels between 20 and
90 percent. Within this range, different charge levels do not affect the
readings. If the battery is insufficiently charged, or has too high a charge, a
message appears and the analyzer automatically applies the appropriate
charge or discharge to bring the battery within testing range. Charging or
discharging a battery immediately prior to taking the reading does not affect
the Cadex Quicktest™ results.
The reader may ask whether the Cadex Quicktest™ system can also learn
incorrectly. No — once the learning cycles have been completed for a given
battery, the matrix settings are firm and resilient. Testing bad batteries will
not affect the setting.
Spoilage is only possible if a number of bad batteries are purposely put
through the ‘Learn’ program in an attempt to alter the existing matrix. Such
would be the case when scanning a batch of batteries that have not been
properly formatted, have been in prolonged storage, or are of poor quality. To
protect the existing matrix from spoilage when adding learning cycles, the
system checks each new vector reading for its integrity before accepting the
information as a valid reference. Learned readings obtained from defective
batteries are rejected.
If a battery adapter has lost its integrity as part of ‘bad learning’, the matrix
setting can be erased and re-taught. As an alternative, Cadex will make
recommended matrices available on the Internet. Users may also want to
exchange learned matrix information with each other. Copying battery
adapters by inserting a recognized adapter into the analyzer will achieve this.
Another method is ‘Webcasting’ the matrices over the Internet.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery invented? >
Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance or hype? > Article:
Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article: Memory, myth
or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article: Battery testers for
modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel Cell, Is it Ready?
> Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9 > Chapter 10 >
Chapter 11 > Chapter 12 > Chapter 13
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How does the Cadex Quicktest work?
The first stage of the Cadex Quicktest™analysis uses a waveform to gather
battery information under certain stresses, establishing probability levels for the
given battery. Since there are many battery types with several interacting
variables, a set of rules is applied to further evaluate the data. The results are
averaged and an estimated battery capacity is predicted. The initial inference to
categorize the batteries is computed from a set of specialized shapes called
membership functions. These membership functions are unique to every battery
model and are developed using a specialized trend-learning algorithm.
The raw data, consisting of three or more items, flows through the input layer.
Vectors leading from the input layer are weighted and the derived values are
passed through a function in the hidden layer. Another vector set channels the
information to the output.
Figure 13-3: Flowchart of a neuro-network based on fuzzy logic.
The first three circles on the left are the inputs. The data entering is ‘fuzzified’
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according to a set of curves called membership functions. A set of rules that
depend on fixed knowledge is evaluated. The results of the rules are combined
and distilled, or ‘defuzzified’. The result is a crisp, non-fuzzy number.
The weights are highly significant and function as the learning facility of the
network. A run would proceed with a certain set of weights. If the result is off by
a certain range, the weights are changed and the process is repeated until a certain
number of iterations have passed or the algorithm produces the correct output.
The Cadex Quicktest™ requires
less time than most other
methods. While current quick test
systems, such as those used in
defense applications, need
hundreds of learning cycles and
run on large computers, the Cadex
method requires minimal
experience and can be performed
on relatively simple hardware. Typically less than five learning cycles are
necessary to achieve robust, model-specific solution sets, also known as matrices.
This massive reduction in time is the result of a new self-learning algorithm that
acquires numerous measures of the battery’s characteristics. The algorithm uses a
unique decision-making formula that determines the best solution set for each
battery model.
Of course, artificial intelligence is a complicated subject, and is beyond the scope
of this book. With respect to complexity, Dr. Lofti Zadeh spoke these famous
words: “As complexity rises, precise statements lose meaning and meaningful
statements lose precision.”
Battery quick testing has raised the interest of manufacturers and users alike. The
race is on to provide a product that is accurate, easy to use and cost effective. The
true winner may not be an individual or organization that amasses the largest
number of patents, but a company that can offer a product that is cost effective
and truly works.
Battery Testing and the Internet
Increasingly, the Internet plays a pivotal role in battery testing. The ability to send
all battery test results to a central global database is an exciting prospect. With
this information on hand, battery manufacturers would be able to perform battery
analysis based on battery type, geographic area and user pattern. Field failures
could be identified quickly and appropriate corrections implemented.
Another application for the Internet is establishing a global database for all major
battery types, complete with matrix settings. With compatible systems, users
would be able to select and download battery information from a central database.
Batteryshop™, a software product offered by Cadex, provides such a service. The
database lists all common batteries, complete with battery specifications and
matrix information. Point and click technology programs the battery analyzer to
the correct battery parameters.
Collaborating with battery manufacturers enables Cadex to create the most
accurate vector settings. Manufacturers welcome such a system because it reduces
beta testing and puts the manufacturer in closer contact with the battery user. The
aim is to reduce warranty returns and increase customer satisfaction.
Another powerful feature of the Internet is downloading new software for
hardware upgrades. Since battery quick testing is still in its infancy, improved
software will be made available in the future that allows upgrading existing
equipment with the latest developments.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13
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Electrochemical Impedance
Spectroscopy
Electrochemical Impedance Spectroscopy (EIS) has been used for a number
of years to test the SoH and SoC of industrial batteries. EIS is well suited for
observing reactions in the kinetics of electrodes and batteries. Changes in
impedance readings hint at minute intrusion of corrosion, which can be
evaluated with the EIS methods. Impedance studies using the EIS technology
have been carried out on lead acid, NiCd, NiMH, Li-ion and other
chemistries. EIS test methods are also used to examine the cells on larger
stationary batteries.
In its simplest manifestation, measurements of internal battery resistance can
be taken by applying a load to a battery and observing the current-voltage
characteristics. A secondary load of higher current is applied, again noting the
voltage and current. The current and voltage relationship of the two loads can
be utilized to provide the internal resistance using Ohm’s Law.
Rather than applying two load levels, an AC signal is injected. This AC
voltage floats as a ripple on top of the battery DC voltage and charges and
discharges the battery alternatively. The AC frequency varies from a low
100mHz to about 5kHz. 100mHz is a very low frequency that takes
10 seconds to complete a full cycle. In comparison, 5kHz completes
5000 cycles in one second. At about 1000Hz, the load behaves more like a
DC resistance because the chemistry cannot follow the rapid changes between
charge and discharge pulses. The information about electrolyte mass transport
is ascertained at lower frequencies.
Additional information regarding the battery’s condition can be obtained by
applying various frequencies. One can envision going through different layers
of the battery and examining each level. Similar to tuning the dial on a
broadcast radio, in which individual stations offer different types of music, so
too does the battery provide different information of the internal processes.
The EIS is an effective technique to analyze the mechanisms of interfacial
structure and to observe the change in the formation when cycling the battery
as part of everyday use.
When applying a sine wave to a
battery, a phase shift between
voltage and current occurs. The
reactive load of the battery causes
this phenomenon. The overall
battery resistance consists of
three resistance types: pure
resistance, inductance and
capacitance. Capacitance is
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responsible for the capacitor effect; and the inductance is accountable for the
so-called magnetic field, or coil effect. The voltage on a capacitor lags behind
the current. This process is reversed on a coil and the current lags behind the
voltage. The level of phase shift that occurs when applying a current through
a reactive load is used to provide information as to the battery’s condition.
One of the difficulties with the EIS method is interpreting the information. It
is one thing to amass a large amount of data, and another to make practical
use of it. Although the derived information reflects aging and other
deficiencies, the readings are not universal and do not apply in the same way
to all battery makes and types. Rather, each battery type generates its own set
of signatures. Without a library of well-defined reference readings with which
to compare, the EIS method has little meaning.
Modern technology can help. The vector settings of a given battery type can
be stored in the test instrument and translated into meaningful readings by
software. The readings can further be analyzed by coupling impedance
spectroscopy with a fuzzy neuro-adaptive algorithm.
Electrochemical Impedance Spectroscopy is commonly used to research
batteries in a lab environment. Best results are obtained on a single cell. EIS is
also used in aviation and in-flight analysis of satellite batteries. Closer to
earth, the EIS method examines stationary batteries for grid corrosion and
water loss. Further refined, the EIS technology has the potential for wider
applications, such as testing portable batteries. EIS may one day test batteries
in a matter of seconds and achieve higher accuracy than current methods.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3
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Part Three
Knowing Your Battery
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or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
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Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14
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Chapter 14: Non-Correctable
Battery Problems
Non-correctable battery problems are those that cannot be improved through
external means such as giving the battery a full charge or by applying
repeated charge/discharge cycles. Deficiencies that denote the non-correctable
status are high internal resistance, elevated self-discharge, electrical short of
one or several cells, lack of electrolyte, oxidation, corrosion and general
chemical breakdown. These degenerative effects are not only caused by
normal usage and aging, but they include less than ideal field conditions and
an element of neglect. The user may have poor charging equipment, may
operate and store the battery in adverse temperatures and, in the case of
nickel-based batteries, may not maintain the battery properly.
New battery packs are not exempt from deficiency syndromes and early
failure. Some batteries may be kept in storage too long and sustain age-related
damage, others are returned by the customer because of incorrect user
preparation.
In this section we examine the cause of non-correctable battery problems and
explore why they occur. We also look at ways to minimize premature
failure.High Self-discharge
Self-discharge is a natural phenomenon of any battery. It is not a
manufacturing defect per se, although poor manufacturing practices and
improper maintenance and storage by the consumer enhance the problem.
The level of self-discharge differs with each chemistry and cell design.
High-performance nickel-based batteries with enhanced electrode surface area
and super conductive electrolyte are subject to higher self-discharge than the
standard version cell with lower energy densities. Self-discharge is non linear
and is highest right after charge when the battery holds full capacity.
NiCd and NiMH battery chemistries exhibit a high level of self-discharge. If
left on the shelf, a new NiCd loses about 10 percent of its capacity in the first
24 hours after being removed from the charger. The rate of self-discharge
settles to about 10 percent per month afterwards. At a higher temperature, the
self-discharge rate increases substantially. As a rule, the rate of self-discharge
doubles with every 10°C (18°F) increase in temperature. The self-discharge of
the NiMH is about 30 percent higher than that of the NiCd.
A major contributor to high self-discharge on nickel and lead-based batteries
is a high cycle count and/or old age. With increased cycles, the battery plates
tend to swell. Once enlarged, the plates press more firmly against the delicate
separator, resulting in increased self-discharge. This is common in aging
NiCd and NiMH batteries but can also be seen in lead acid systems.
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Loading less active materials on the plates can reduce the plate swelling on
nickel-based batteries. This improves expansion and contraction while
charging and discharging. In addition, the load characteristic is enhanced and
the cycle life prolonged. The downside is lower capacity.
Metallic dendrites penetrating into the separator are another cause of high
self-discharge. The dendrites are the result of crystalline formation, also
known as memory. Once marred, the damage is permanent. Poorly designed
chargers that ‘cook’ the batteries also increase the self-discharge. High cell
temperature causes irreversible damage to the separator.
While the nickel-based systems can withstand some abuse and tolerate
innovative or crude charge methods, the Li-ion demands tight charging and
discharging regimes. Keeping the voltage and current within firm boundaries
prevents the growth of dendrites. The presence of dendrites in lithium-based
batteries has more serious implications than just an increase in self-discharge
— dendrites can cause an electrical short, which could lead to venting with
flame.
The self-discharge of the Li-ion battery is five percent in the first 24 hours
after charge and averages 1 to 2 percent per month thereafter. In addition to
the natural self-discharge through the chemical cell, the safety circuit draws as
much as 3 percent per month. High cycle count and aging has little effect on
self-discharge on lithium-based batteries.
An SLA self-discharges at a rate of only five percent per month or 50 percent
per year. Repeated deep cycling increases the self-discharge. When deep
cycling, the electrolyte is drawn into the separator, resulting in a crystalline
formation similar to that of a NiCd battery.
The self-discharge of a battery is best measured with a battery analyzer. The
procedure starts by charging the battery. The capacity is read by applying a
controlled discharge. The battery is then recharged and put on a shelf for
24 hours, after which the capacity is measured again. The discrepancy
between the capacity readings reveals the level of self-discharge.
More accurate self-discharge measurements can be obtained by allowing the
battery to rest for at least 72 hours before taking the reading. The longer rest
period compensates for the relatively high self-discharge immediately after
charge. At 72 hours, the self-discharge should be between 15 and 20 percent.
The most uniform self-discharge readings are obtained after seven days. On
some battery analyzers, the user may choose to adjust the desired rest periods
in which the self-discharge is measured.
Research is being conducted to find a way to measure the self-discharge of a
battery in minutes, if not seconds. The accuracy and repeatability of such
technology is still unknown. The challenge is finding a formula that applies to
all major batteries and includes the common chemistries.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
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> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14
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Low Capacity Cells
Even with modern manufacturing techniques, the capacity of a cell cannot be
accurately predicted. As part of the manufacturing process, each cell is
measured and segregated into categories according to their inherent capacity
levels. The high capacity A cells are commonly sold for special applications
at premium prices; the large mid-range B cells are used for commercial and
industrial applications such as mobile communications; and the low-end C
cells are mostly sold in supermarkets at bargain prices. Cycling will not
significantly improve the capacity of the low-end cell. When purchasing
rechargeable batteries at a reduced price, the buyer should be aware of the
different capacity and quality levels offered.
As part of quality control, the battery assembler should spot-check each batch
of cells to examine cell uniformity in terms of voltage, capacity and internal
resistance. Failing to observe these simple rules will often result in premature
battery failures. When buying quality cells from a well-known manufacturer,
battery assemblers are able to relax the matching requirements somewhat.
Cell Mismatch
Cell mismatch can be found in brand-new as well as aged battery packs. Poor
quality control at the cell manufacturing level and inadequate cell matching
when assembling the batteries cause unevenly matched cells. If only slightly
off, the cells in a new pack adapt to each other after a few charge/discharge
cycles, like players in a winning sports team.
A weak cell holds less capacity and is discharged more quickly than the
strong one. This imbalance causes cell reversal on the weak cell if the battery
is discharged below 1V/cell. The weak cell reaches full charge first and goes
into heat-generating overcharge while the stronger cell still accepts charge
and remains cool. In both situations, the weak cell is at a disadvantage,
making it weaker and contributing to a more acute cell mismatch condition.
An analogy can be made with a high school bully who picks on the weaker
kid.
High quality cells are more consistent in capacity than lower quality
counterparts. During their life span, high quality cells degrade at about the
same rate, helping to maintain the matching. Manufacturers of power tools
choose high quality cells because of their durability under heavy load
conditions and temperature extremes. Lower-cost cells have been tried, but
early failure and consequent replacement is costlier than the initial
investment.
The capacity matching between the cells in a battery pack should be within
+/- 2.5 percent. Tighter tolerances are required on batteries with high cell
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counts that also must generate high load currents and are operating under
adverse temperatures. There is a strong correlation between well-balanced
cells and the longevity of a battery.
Lithium-based cells have tighter matching tolerances than their nickel-based
cousins. Tight matching of all cells in a pack is especially important on
lithium-based chemistries. All cells must reach the end-of-discharge voltage
threshold at the same time. The full-charge point must be attained in unison
by all cells. If the cells are allowed to get out of match, the weaker cell will be
discharged to a lower voltage point before the cut-off occurs. On charge, this
weak cell will attain the full-charge status before the others, causing the
voltage to go higher than on the stronger cells. This larger voltage swing will
put undue strain on the weak cell.
Each cell in a lithium-based pack is electronically monitored to assure proper
cell matching during the battery’s life. An electronic circuit is added to some
packs that compensate the differences in cell voltages. This is done by
connecting a shunt across each cell string to consume the excess energy of the
cells which are more energetic. The low-voltage cut-off occurs when the
weakest cell reaches the end-of-discharge point.
The Li-ion battery is controlled down to the cell level to assure safety at all
times. Because this chemistry is still relatively new and unpredictable under
extreme conditions, manufacturers do not want to take undue risks. There
have been a few failures but such irregularities are often kept a secret. This
chemistry is considered very safe, considering the large number of Li-ion
batteries that are in use.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14
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Shorted Cells
Manufacturers are often unable to explain why some cells develop high
electrical leakage or an electrical short while the batteries are still relatively
new. There are a number of possible reasons that contribute to this irreversible
form of cell failure.
The suspected culprit is foreign particles that contaminate the cells during
manufacture. Another possible cause is rough spots on the plates that damage
the separator. Better quality control at the raw material level and minimal
human interface during the manufacturing process has greatly reduced the
‘infant mortality’ rate of the modern rechargeable cells.
Cell reversal caused by deep discharging also contributes to shorted cells.
This commonly occurs if a nickel-based battery is being fully depleted under
a heavy load. A NiCd battery is designed with some reverse voltage
protection and a small reverse current in the magnitude of milliamperes can
be tolerated. A high current, however, causes the reversed-polarized cell to
develop a permanent electrical short. Another cause of a short circuit is
marring the separator through uncontrolled crystalline formation.
Applying momentary high-current bursts in an attempt to repair shorted cells
has had limited success. The short may temporarily evaporate but the damage
to the separator material remains. The repaired cell often exhibits a high
self-discharge and the short frequently returns.
Replacing a shorted cell in an aging pack is not recommended unless the new
cell is matched with the others in terms of voltage and capacity. Otherwise, an
imbalance may occur. One may remember the biblical verse “No one puts a
patch of unshrunken cloth on an old garment. . .” or “No man would put new
wine into old wineskins. . .” (Mt 9.16-17). Attempts to replace faulty cells
have commonly lead to battery failures after about six months of use. It is best
not to disturb the cells in a battery pack but allow them to age naturally.
Maintaining the batteries while they are still in good working condition will
help to prevent premature failure.
Shorts in a Li-ion cell are uncommon. Protection circuits monitor an ailing
Li-ion cell and render the pack unusable if serious voltage irregularities are
detected. Charging such a pack would (protection circuit permitting) generate
excess heat. The battery’s temperature control circuits are designed to
terminate the charge.
Loss of Electrolyte
Although sealed, battery cells may lose some electrolyte during their life.
Typical loss of moisture occurs if the seal opens due to excessive pressure.
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This occurs if the battery is charged at very low or very high temperatures.
Once vented, the spring-loaded seal of nickel-based cells may never properly
close again, resulting in a deposit of white powder around the seal opening.
Losses may also occur if the cell cap is not correctly sealed in the
manufacturing process. The loss of electrolyte results in a decrease of
capacity, a defect that cannot be corrected.
Permeation, or loss of electrolyte in sealed lead acid batteries, is a recurring
problem. Overcharge is the main cause. Careful adjustment of charging and
float voltages reduces loss of electrolyte. In addition, the battery should
operate at moderate temperatures. Air-conditioning is a prerequisite for
VRLA batteries, especially in warmer climates.
Replenishing lost liquid in VRLA batteries by adding water has had limited
success. Although lost capacity can often be regained with a catalyst, the
performance of the stack is short-lived. After tampering with the cells, it was
observed that the battery stack turned into high maintenance mode and needed
to be closely supervised.
A properly designed, correctly charged Li-ion cell should never generate
gases. As a result, the Li-ion battery does not lose electrolyte through venting.
But in spite of what is being said, the lithium-based cells can build up an
internal pressure under certain conditions. Provisions are made to maintain
safety of the battery and equipment should this occur. Some cells include an
electrical switch that opens if the cell pressure reaches a critical level. Other
cells feature a membrane that safely releases the gases if need be. Controlled
release of the pressure prevents bulging of the cell during pressure buildup.
Most of the safety features of lithium-based batteries are one-way; meaning
that once activated, the cells are inoperable thereafter. This is done for safety
reasons.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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Chapter 15: Caring for Your
Batteries from Birth to
Retirement
It is interesting to observe that batteries cared for by a single user generally
last longer than those that operate in an open fleet system where everyone has
access to, but no one is accountable for them. There are two distinct groups of
battery users — the personal user and the fleet operator.
A personal user is one who
operates a mobile phone, a
laptop computer or a video
camera for business or
pleasure. He or she will most
likely follow the
recommended guidelines in
caring for the battery. The
user will get to know the
irregularities of the battery.
When the runtime gets low, the battery often gets serviced or replaced.
Critical failures are rare because the owner adjusts to the performance of the
battery and lowers expectations as the battery ages.
The fleet user, on the other hand, has little personal interest in the battery and
is unlikely to tolerate a pack that is less than perfect. The fleet user simply
grabs a battery from the charger and expects it to last through the shift. The
battery is returned to the charger at the end of the day, ready for the next
person. Little or no care is given to these batteries. Perhaps due to neglect,
fleet batteries generally have a shorter service life than those in personal use.
How can fleet batteries be made to last longer? An interesting contrast in the
handling of fleet batteries can be noted by comparing the practices of the
US Army and the Dutch Army, both of which use fleet batteries. The
US Army issues batteries with no maintenance program in place. If the battery
fails, another pack is issued. Little or no care is given and the failure rate
is high.
The Dutch Army, on the other hand, has moved away from the open fleet
system by making the soldiers responsible for their batteries. This change was
made in an attempt to reduce battery waste and improve reliability. The
batteries are issued in the soldier’s name and the packs become part of their
personal belongings. The results are startling. Since the Dutch Army adapted
this new regime, the failure rate has dropped considerably and, at the same
time, battery performance has increased. Unexpected down time has almost
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been eliminated.
It should be noted that the Dutch Army uses exclusively NiCd batteries. Each
pack receives periodic maintenance to prolong service life. Weak batteries are
systematically replaced. The US Army, on the other hand, uses NiMH
batteries. They are evaluating the Li-ion polymer for the next generation
battery.
Because of the high failure rate of fleet batteries and the uncertain situations
such failures create, some organizations assign a person to maintain batteries.
This person checks all batteries on a scheduled basis, exercises them for
optimum service life, and replaces those that fall below an accepted capacity
level and do not recover with maintenance programs. Batteries perform an
important function; giving them the care they deserve is appropriate.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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Storage
Batteries are a perishable product and start deteriorating right from the time
they leave the manufacturing plant. For this reason, it is not advisable to stock
up on batteries for future use. This is especially true with lithium-based
batteries. The buyer should also be aware of the manufacturing date. Avoid
acquiring old stock.
Keep batteries in a cool and
dry storage area.
Refrigerators are
recommended, but freezers
must be avoided because
most battery chemistries are
not suited for storage in
sub-freezing temperatures.
When refrigerated, the
battery should be placed in a plastic bag to protect it against condensation.
The NiCd battery can be stored unattended for five years and longer. For best
results, a NiCd should be fully charged, then discharged to zero volts. If this
procedure is impractical, a discharge to 1V/cell is acceptable. A fully charged
NiCd that is allowed to self-discharge during storage is subject to crystalline
formation (memory).
Most batteries are shipped with a state-of-charge (SoC) of 40 percent. After
six months storage or longer, a nickel-based battery needs to be primed before
use. A slow charge, followed by one or several discharge/charge cycles, will
do. Depending on the duration of storage and temperature, the battery may
require two or more cycles to regain full performance. The warmer the storage
temperature, the more cycles will be needed.
The Li-ion does not like prolonged storage. Irreversible capacity loss occurs
after 6 to 12 months, especially if the battery is stored at full charge and at
warm temperatures. It is often necessary to keep a battery fully charged as in
the case of emergency response, public safety and defense. Running a laptop
(or other portable device) continuously on an external power source with the
battery engaged will have the same effect. Figure 15-1 illustrates the
recoverable capacity after storage at different charge levels and temperatures.
The combination of a full charge condition and high temperature cannot
always be avoided. Such is the case when keeping a spare battery in the car
for a mobile phone. The NiMH and Li-ion chemistries are most severely
affected by hot storage and operation. Among the Li-ion family, the cobalt
has an advantage over the manganese (spinel) in terms of storage at elevated
temperatures.
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Temperature 40% charge level
(recommended storage charge
level)
100% charge level
(typical user charge
level)
0°C
98% after 1 year
94% after 1 year
25°C
96% after 1 year
80% after 1 year
40°C
85% after 1 year
65% after 1 year
60°C
75% after 1 year
60% after 3 months
Figure 15-1: Non-recoverable capacity loss on Li-ion batteries after storage.
High charge levels and elevated temperatures hasten the capacity loss.
Improvements in chemistry have increased the storage performance of some
Li-ion batteries.
The recommended storage temperature of a lithium-based battery is 15°C
(59°F) or less. A charge level of 40 percent allows for some self-discharge
that naturally occurs; and 15°C is a practical and economical storage
temperature that can be achieved without expensive climate control systems.
While most rechargeable batteries cannot be stored at freezing temperatures,
some newer commercial Li-ion batteries can be kept at temperatures of -40°C
without apparent side effects. Such temperature tolerances enable long and
cost-effective storage in the arctic.
The SLA battery can be stored for up to two years but must be kept in a
charged condition. A periodic topping charge, also referred to as ‘refreshing
charge’, is required to prevent the open cell voltage from dropping below
2.10V. (Depending on the manufacturer, some lead acid batteries may be
allowed to drop to lower voltage levels). When self-discharged below a
critical voltage threshold, sulfation occurs on most lead acid batteries.
Sulfation is an oxidation layer on the negative plate that alters the charge and
discharge characteristics. Although cycling can often restore the capacity loss,
the battery should be recharged before the open cell voltage drops below
2.10V.
The SLA cannot be stored below freezing temperatures. Once a pack has been
frozen, it is permanently damaged and its service life is drastically reduced. A
previously frozen battery will only be able to deliver a limited number of
cycles.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
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Priming
Some nickel-based batteries do not perform well when new. This deficiency is
often caused by lack of formatting at the time of manufacturing. Batteries that
are not sufficiently formatted are destined to fail because the initial capacity is
low. The full potential is only reached after the battery has been cycled a few
times. In many cases, the user does not have the patience to wait until the
expected performance is reached. Instead, the customer exercises the warranty
return option.
The most critical time in a battery’s life is the so-called priming stage. An
analogy can be drawn with breaking in a new car engine. The performance
and fuel efficiency may not be best at first, but with care and attention, the
engine will improve over time. If overstressed when new, the engine may
never provide the economical and dependable service that is expected.
Some poorly formatted batteries are known to produce less than 10 percent of
capacity at the initial priming stage. By cycling, the capacity increases, and
the battery will become usable after three to five cycles. Maximum
performance on a NiCd, for example, is reached after 50 to 100 full
charge/discharge cycles. This priming function occurs while the battery is
being used. The gradual capacity increase during the early life of a battery is
normally hidden to the user.
Quality cells from major Japanese manufacturers do not need extended
priming and can be used almost immediately. After five full cycles, the
performance is predictable and fully repeatable.
The manufacturer’s recommended priming procedure should be followed. In
many cases, a 24-hour trickle charge is needed. Verifying the performance
with a battery analyzer is advisable, especially if the batteries are used for
critical applications.
Some nickel-based batteries are known to form a passivation layer if kept in
prolonged storage. Little scientific knowledge is available on this subject and
the battery manufacturers may deny the existence of such a layer. A full
charge/discharge, followed by a complete recharge corrects the problem.
Li-ion cells need less priming than the nickel-based equivalent. Manufacturers
of Li-ion cells insist that priming is not a requirement. The priming function
on the Li-ion may be used to verify that the battery is fully functional and
produces the capacity required.
In an earlier chapter, the question “Why are excessive quantities of batteries
being returned under warranty?” was raised. This question has not been fully
answered. It appears that all battery chemistries are represented among the
packs being returned. It is unclear whether these batteries are inoperable as
claimed. Perhaps the liberal warranty return offered by dealers provides an
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opportunity to acquire a new, and seemingly better, battery without charge.
Some misuse of the warranty policy cannot be fully dismissed.
The internal protection circuit of lithium-based batteries may be the cause of
some problems. For safety reasons, many of these batteries do not allow a
recharge if the battery has been discharged below 2.5V/cell. If discharged
close to 2.5V and the battery is not recharged for a while, self-discharge
further discharges the pack below the 2.5V level. If, at this time, the battery is
put into the charger, nothing may happen. The battery appears to have an open
circuit and the user consequently demands a replacement.
Cadex has received a large number of supposedly dead Li-ion polymer
batteries from various manufacturers. When measured, these batteries had no
voltage at the terminals and appeared to be dead. Charging the packs in their
respective chargers was unsuccessful. But after waking up the battery’s
control circuit with the ‘Boost’ function of the Cadex 7000 Series battery
analyzer, most of these batteries accepted normal charge. After a full charge,
the performance was checked. Almost all packs reached capacities of
80 percent and higher and the batteries were returned to service.
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Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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The Million Dollar Battery Problem
In today’s surging mobile phone market, many batteries are returned to
mobile phone carriers before the ink on the invoice has dried. The most
common consumer complaint is ‘less than expected’ runtime.
The reasons for this failure are multi-fold. The battery may not have been
properly formatted at the factory. Perhaps the packs remained on the shelf too
long or have been discharged too low. Incorrect customer preparation is also
to blame. The true reason for such failure may never be known.
Dealers are not equipped to handle
the influx of returned batteries. To
fulfill the warranty obligations and
satisfy the customer, the dealer
hands out a new battery and sends
the faulty pack to the manufacturer.
Truckloads of ‘worthless’ batteries
are transported, only to be stockpiled
in warehouses for eventual testing or
recycling at the manufacturer’s expense. The cost of exchange, time lost by
retail staff, shipping, warehousing and eventual disposal amounts to a million
dollar problem.
On a recent visit to Europe, a Cadex staff member learned that a large phone
manufacturer had received 17 tons of failed handset batteries in one year
alone. The batteries were stockpiled in large barrels for recycling. He also
discovered that 15,000 NiMH batteries were returned to the manufacturer
within weeks after the release of a new phone. When spot-checking the failed
batteries with a Cadex 7000 Series battery analyzer, most packs appeared to
be operational.
On another occasion, a total of 14,000 Li-ion batteries were returned to a
North American mobile phone provider. Of these, only 700 (or 5 percent),
were faulty. Of these, ten random batteries were sent to Cadex for further
testing. The Cadex lab reported that each of these failed packs indeed had
genuine faults.
A European service center sent 40 Li-ion polymer batteries to Cadex for
evaluation. These packs had failed in the field and were returned to the
service center by customers. When servicing the batteries on a Cadex 7000
Series battery analyzer, 37 units were found to be fully functional with
capacities of above 80 percent and impedances below 180mW.
Phone manufacturers report that 80 to 90 percent of returned batteries have no
faults or can easily be repaired with battery analyzing equipment. The
remaining 10 to 20 percent, which do not easily recover with basic service,
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can often be restored with extended programs. Only a small percentage of
batteries returned under warranty exhibit non-correctable faults.
Not all batteries and portable equipment under warranty fail due to
manufacturer’s defects. A service manager for a major mobile phone
manufacturer hinted that submersion into a cup of coffee or soft drink is a
sizable contributor to equipment and battery failures. Apparently, the acids in
the beverages manage to corrode the electrical conductors. Submersion into
coffee occurs when the user mistakes the coffee cup for the phone cradle.
In an effort to salvage returned batteries, a leading mobile phone
manufacturer segregates battery packs according to purchase date. Packs
returned within the thirty-day warranty period are marked as type B. The
batteries are then sent to a regional service center where they are serviced
with battery analyzers. If the batteries are clean, (have no coffee residue) and
regain a capacity of 80 percent or higher, the packs are relabeled and sold as a
B class product. Over 90 percent of their returned batteries have been
reclaimed with this program.
On the strength of this success, some battery-refurbishing houses have
extended the service to include batteries of up to one year old. The service
center experiences a 40 to 70 percent restoration yield in repairing these older
batteries. The battery-refurbishing centers are said to make a profit. Equally
important, such programs reduce the environmental impact of battery
disposal.
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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To the Service Counter, and No
Further
Not all manufacturers and dealers offer battery-refurbishing centers. If not
available, a program is gaining popularity in which the battery is serviced at
the store level. When a customer returns a faulty battery, the pack goes no
further than the store that sold the equipment.
The customer service clerk checks the battery on site with approved test
equipment. An attempt is made to restore the battery. If not successful and a
warranty replacement is needed, a service report is issued, which is sent to the
manufacturer by fax or e-mail. After verifying the report, the manufacturer
offers replacement batteries as part of the warranty replacement policy.
Warranty replacement can be further streamlined by using the Internet and
compatible battery analyzers. Such a process will operate with a minimum of
human resources and run independent of office hours and time zones. Here’s
how it works:
The manufacturer first sends each participating store an appropriate number
of replacement batteries. When a customer returns a faulty battery, service
personnel test the pack with the in-store analyzer. If restoration is
unsuccessful, the analyzer e-mails a report to the manufacturer, stating the
nature of the deficiency. Other information, such as the date of purchase,
battery type and customer name are also included. The computer at the
manufacturer’s headquarters verifies the claim and, if valid, issues an
inventory adjustment against the spare batteries allocated to the store. When
the stock gets low, a re-stocking order is generated and additional batteries are
sent out automatically.
Besides lowering overhead
costs, a fully integrated warranty
replacement system provides the
manufacturer with accurate
information regarding the nature
of battery failures. User patterns
leading to battery failure can be
evaluated by geographic region.
For example, a temperature
related failure might be more
likely to occur in warm climates than in cool ones. Batteries with higher
temperature resiliency can be allocated for these regions. Recurring problems
can be identified quickly and corrective measures implemented within months
rather than years. Such measures can be as simple as providing the customer
with better operating instructions in preparing a new battery before use.
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One of the most difficult problems in servicing batteries at store-level is a lack
of technical know-how by the customer service personnel. With the
ever-increasing number of battery models, the task of identifying a battery
type and setting the correct parameters is becoming increasingly more
complex. Technology is not keeping pace in supplying the battery market
with suitable test equipment that is both cost effective and easy to use.
To bring battery testing within reach of the untrained user, battery analyzers
must be simple to operate and allow easy interface with all major battery
types. Setting the correct battery parameters should be clear and concise.
Uncertainties that can lead to errors must be minimized. The manufacturer of
the battery test equipment should be aware that the task of operating a battery
analyzer is not part of the clerk’s job description.
The Batteryshop™ software by Cadex has been developed for the purpose of
simplifying battery maintenance. When installed in a PC, the operator simply
selects the desired battery from the database of over 2000 battery listings.
With the Cadex 7000 Series connected to the PC, the analyzer programs itself
to the correct parameters with the click of the mouse. The user only needs to
insert the battery into the appropriate battery adapter and everything else is
done automatically.
Some batteries, such as those manufactured by Motorola, are equipped with
bar code labels. If bar coded, the user can simply scan the bar code label and
insert the battery into the analyzer. Here is how it works:
The scanned battery model number is matched with the battery listing in the
database. Cadex Batteryshop™ then assigns the appropriate battery
configuration code (C-code) to the battery and downloads it to the Cadex
7000 Series. The analyzer is now programmed to the correct parameters,
ready to service the battery.
Not all battery packs come with bar code identification. If not available, a
label printer connected to the PC can generate the missing bar code. These
labels can be attached to a separate sheet on the service counter. The bar code
labels may also be placed next to an illustration of the battery. The clerk
simply refers to the correct battery and scans the bar code label associated
with the battery. The system is now set to service the battery.
In the near future it will be possible to view the picture of the battery on the
PC monitor. Clicking the mouse on the image will reveal all model numbers
associated with this battery. A click on the correct model will program the
analyzer.
When training global staff, simplification and automation make common
sense. With tools now available that do the thinking, employees no longer
need to be battery experts. Similar to a checkout clerk in a supermarket who,
in the pre-computer days, required full product knowledge can now rely on
the embedded bar code information. The price of all items purchased is
flashed on the screen and an up-to-the-second inventory status is available.
Such simplifications are also possible in servicing commercial batteries.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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The Quick Fix
Checking a battery and assessing its status within a few minutes is one thing
— finding a solution and actually fixing the problem is another. Increasingly,
customers and dealers alike are seeking an alternative solution to replacing the
batteries under warranty. They want a quick fix.
Fully automated test procedures are being developed which check the battery
and apply a quick-prime program to wake up a sleeping battery. The program
will last from a few minutes for an easy wake-up call, to an hour or longer for
the deep-sleepers.
Batteries with minor deficiencies will be serviced while the customer enjoys a
cup of coffee or browses through the store. If the battery has an electrical
short or does not accept a charge, the likelihood of revitalizing the battery is
slim. This pack is eliminated within seconds to clear the test equipment for
other batteries. If a pack requires extensive priming, which will take a
few hours to complete, the customer is asked to come back later.
Some battery analyzers
indicate the estimated service
time after the battery has
passed through the early
assessment stages. The
customer can decide to wait,
buy a spare battery, or come
back for the repaired battery
the next day.
A complete battery cycle offers the best service. Such a service makes optimal
use of the restorative abilities of a battery analyzer. A full cycle may take five
to eight hours and can be applied overnight. Multi-bay analyzers that service
several batteries at the same time increase the throughput. Such analyzers
operate 24 hours without user intervention.
A customer may not have time to wait for the outcome of a battery test. The
prospect of having to buy a new battery is even less appealing. In such a case,
a class B or replacement battery may be the answer. This pack can be drawn
from a pool of refurbished batteries, which the store has built up from
previous returns. This could become a lucrative side business as customers
begin to realize the cost saving potential, especially if the battery is
accompanied by a performance report.
Some battery analyzers offer ultra-fast charge functions. The maximum
permissible charge current that can be applied to a battery is dictated by the
battery’s ability to absorb charge. A fit battery, or one that has a partial
charge, would charge to the 70 percent level in 30 minutes or less. A
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70 percent charge level is often sufficient to complete a performance test or
quick-fill the battery for a hurried customer. The topping charge from there to
full charge is what demands the long charge time.
Some late model battery analyzers also offer a quick priming program that
services a battery in a little more than an hour. This program applies an
ultra-fast charge and ultra-fast discharge to check the integrity of the battery.
By virtue of cycling, some priming and conditioning activities occur.
Customers demand a quick turnaround when a mobile phone fails.
Manufacturers and service providers realize that better methods are needed to
handle customer returns. The expensive and wasteful battery exchange
policies practiced today may no longer be acceptable in the future. Fierce
competition and tight product margins are part of the reason. Returned
batteries account for a considerable after-sale burden. With modern
technology, these costs can be reduced while improving customer service and
enhancing satisfaction.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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Battery Warranty
Some manufacturers of industrial batteries provide warranties of up to
18 months. A free exchange is offered if the battery fails to meet 80 percent of
the rated capacity throughout the warranty period. (I hasten to mention that
these warranty policies apply to markets other than mobile phones.)
But what happens if such a battery is returned for warranty? Will the dealer
replace the pack without hesitation? Rarely.
With lack of battery standards, manufacturers are free to challenge warranty
claims, even if a genuine problem exists. Many batteries reveal only the
chemistry and voltage on the label and do not make reference to the
milliampere-hour rating (mAh). How does the user know what capacity rating
to use when testing the battery? What performance standards can be applied?
On battery packs that show the mAh rating, some battery manufacturers may
have used the peak capacity rating. This is done for promotional reasons to
make their packs look better than the competitor’s. Peak capacity is based on
a lower discharge rate because a battery produces higher readings if
discharged slowly. For warranty purposes, a discharge of 1C should be used.
Regulatory authorities stress the importance of marking all batteries with the
average capacity rating. Portable batteries with a capacity of up to about 2A
should be rated at a 1C discharge. Batteries above that capacity may be rated
at 0.5C. No true standard exists in term of capacity rating.
With the increased popularity of battery analyzers, battery manufacturers and
dealers are urged to follow industry-accepted standards regarding battery
ratings. In an attempt to lower warranty claims, some battery manufacturers
have moderated the published ratings of some batteries to be more consistent
with reality.
Manufacturers are concerned about the high cost of providing free
replacement batteries and disposing of returned units. If a battery analyzer is
used, failures due to fading capacity can mostly be corrected. Warranty claims
are exercised only on those packs that develop a genuine failure. If fewer
batteries returned, the vendor can offer better pricing.
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Copyright 2001 Isidor Buchmann. All rights reserved.
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Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15
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Battery Recycling
Even though the emphasis in battery research has shifted away from NiCd to
newer technologies, the NiCd battery continues to be one of the most used
rechargeable batteries. Over 75 million NiCd batteries were sold in the US
during the year 2000. Market reports indicate that the demand of NiCd
batteries is expected to rise six percent per year until 2003. The demand for
other chemistries, such as the NiMH and Li-ion family, is rising at a more
rapid pace. Where will the mountains of batteries go when spent? The answer
is recycling.
The lead acid battery has led
the way in recycling. The
automotive industry should
be given credit in organizing
ways to dispose of spent car
batteries. In the USA,
98 percent of all lead acid
batteries are recycled.
Compared to aluminum cans (65 percent), newspaper (59 percent) and glass
bottles (37 percent), lead acid batteries are reclaimed very efficiently, due in
part to legislation.
Only one in six households in North America recycle rechargeable batteries.
Teaching the public to bring these batteries to a recycling center is a
challenging task. Homeowners have the lowest return ratios, but this should
improve once more recycling repositories become available and better
environmental awareness is emphasized.
Careless disposal of the NiCd is very hazardous to the environment. If used in
landfills, the cadmium will eventually dissolve itself and the toxic substance
will seep into the water supply, causing serious health problems. Our oceans
are already beginning to show traces of cadmium (along with aspirin,
penicillin and antidepressants) but the source of the contamination is
unknown.
Although NiMH batteries are considered environmentally friendly, this
chemistry is also being recycled. The main derivative is nickel, which is
considered semi-toxic. NiMH also contains an electrolyte that, in large
amounts, is hazardous to the environment.
If no disposal service is available in an area, individual NiMH batteries can be
discarded with other household wastes. If ten or more batteries are
accumulated, the user should consider disposing the batteries in a secure
waste landfill.
Lithium (metal) batteries contain no toxic metals, however, there is the
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possibility of fire if metallic lithium is exposed to moisture while the cells are
corroding. Most lithium batteries are non-rechargeable and are used by
defense organizations. For proper disposal, these batteries must be fully
discharged in order to consume all the metallic lithium content. Li-ion
batteries do not contain metallic lithium and the disposal problem does not
exist. Most lithium systems, however, contain toxic and flammable
electrolyte.
In 1994, the Rechargeable Battery Recycling Corporation (RBRC) was
founded to promote the recycling of rechargeable batteries in North America.
RBRC is a non-profit organization that collects batteries from consumers and
businesses and sends them to Inmetco and Toxco for recycling. Inmetco
specializes in recycling NiCd, but also accepts NiMH and lead-based
batteries. Toxco, focuses on lithium metal and Li-ion system. Currently only
intended to recycle NiCd batteries, RBRC will expand the program to include
also NiMH, Li-ion and SLA batteries.
Programs to recycle spent batteries have been in place in Europe and Asia for
many years. Sony and Sumitomo Metal in Japan have developed a technology
to recycle cobalt and other precious metals from Li-ion batteries. The rest of
Asia is progressing at a slower rate. Some movements in recycling spent
batteries are starting in Taiwan and China, but no significant infrastructure
exists.
Battery recycling plants require batteries to be sorted according to
chemistries. Some sorting is done prior to the battery arriving at the recycling
plants. NiCd, NiMH, Li-ion and lead acid are often placed in designated
boxes at the collection point.
Sorting batteries adds to the cost of recycling. The average consumer does not
know the chemistry of the batteries they are using. For most, a battery is a
battery.
If a steady stream of batteries, sorted by chemistry, were available at no
charge, recycling would be feasible with little cost to the user. The logistics of
collection, transportation and labor to sort the batteries make recycling
expensive.
The recycling process
starts by removing the
combustible material,
such as plastics and
insulation using a gas
fired thermal oxidizer.
Gases from the thermal
oxidizer are sent to the
plant’s scrubber where
they are neutralized to remove pollutants. The process leaves the clean, naked
cells which contain valuable metal content.
The cells are then chopped into small pieces, which are then heated until the
metal liquefies. Non-metallic substances are burned off; leaving a black slag
on top that is removed with a slag arm. The different alloys settle according to
their weights and are skimmed off like cream from raw milk.
Cadmium is relatively light and vaporizes easily at high temperatures. In a
process that appears like a pan boiling over, a fan blows the cadmium vapor
into a large tube, which is cooled with water mist. This causes the vapors to
condense. A 99.95 percent purity level of cadmium can be achieved using this
method.
Some recyclers do not separate the metals on site but pour the liquid metals
directly into what the industry refers to as ‘pigs’ (65 pounds) or ‘hogs’
(2000 pounds). The pigs and hogs are then shipped to metal recovery plants.
Here, the material is used to produce nickel, chromium and iron re-melt alloy
for the manufacturing of stainless steel and other high end products.
Current battery recycling methods requires a high amount of energy. It takes
six to ten times the amount of energy to reclaim metals from recycled
batteries than it would through other means. A new process is being explored,
which may be more energy and cost effective. One method is dissolving the
batteries with a reagent solution. The spent reagent is recycled without
forming any atmospheric, liquid or solid wastes.
Who pays for the recycling of batteries? Participating countries impose their
own rules in making recycling feasible. In North America, some recycling
plants bill on weight. The rates vary according to chemistry. Systems that
yield high metal retrieval rates are priced lower than those which produce less
valuable metals. The highest recycling fees apply to NiCd and Li-ion batteries
because the demand for cadmium is low and Li-ion batteries contain little in
the way of retrievable metal. The recycling cost of alkaline is 33 percent
lower than that of NiCd and Li-ion because the alkaline cell contains valuable
iron. The NiMH battery yields the best return. Recycling NiMH produces
enough nickel to pay for the process.
Not all countries base the cost of recycling on the battery chemistry; some put
it on tonnage alone. The cost of recycling batteries is about $1,000 to
$2,000US per ton. Europe hopes to achieve a cost per ton of $300US. Ideally,
this would include transportation, however, moving the goods is expected to
double the overall cost. For this reason, Europe sets up several smaller
processing locations in strategic geographic locations.
Significant subsidies are sill required from manufacturers, agencies and
governments to support the battery recycling programs. These subsidies are in
the form of a tax added to each manufactured cell. RBRC is financed by such
a scheme.
Caution: Under no circumstances should batteries be incinerated as this can
cause them to explode.
Important: In case of rupture, leaking electrolyte or any other cause of
exposure to the electrolyte, flush with water immediately. If eye exposure
occurs, flush with water for 15 minutes and consult a physician immediately.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16
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Chapter 16: Practical Battery
Tips
Batteries seem to have a mind of their own. Their stubborn and unpredictable
behavior has left many battery users in awkward situations. In fact, the British
Army could have lost the Falkland War in 1982 because of uncooperative
batteries. The army assumed that a battery would always follow rigid military
specifications. Not so. When the order was given to launch the portable
missiles, nothing happened and the missiles did not fly that day. Such
battery-induced letdowns happen on a daily basis. Some are simply a
nuisance, others have serious consequences.
In this section we examine what the user can reasonably expect from a
battery. We learn how to cope with the many moods of a battery and how to
come to terms with its limitations.
Personal Field Observations
While working with General Electric, I had the opportunity to examine the
behavior of many NiCd batteries for two-way radios. I noticed a trend with
these batteries that was unique to NiCd. These particularities repeated
themselves in various other applications.
A certain organization continually experienced NiCd battery failure after a
relatively short service time. Although the batteries performed at 100 percent
when new, their capacity dropped to 20 percent and below within one year.
We discovered that their two-way radios were under-utilized; yet the batteries
received a full recharge after each short field use.
After replacing the batteries, we advised the organization to exercise the new
batteries once per month by discharging them to one-volt-per cell with a
subsequent recharge. The first exercise took place after the batteries had been
in service for four months. At that stage, we were anxious to find out how
much the batteries had deteriorated. Here is what we found:
On half of the batteries tested, the capacity loss was between 25 to 30 percent;
on the other half, the losses were around 10 to 20 percent. With exercise —
and some needed recondition cycles — all batteries were fully restored. Had
maintenance been omitted for much longer, the probability of a full recovery
would have been jeopardized.
On another occasion, I noticed that two-way radios used by construction
workers experienced fewer NiCd battery problems than those used by security
guards. The construction workers often did not turn off the radios when they
put down their hammers. As a result, the batteries got their exercise and kept
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performing well until they fell apart from old age. In many cases the batteries
were held together with electrician’s tape.
In comparison, the security guards pampered their batteries to death by giving
them light duty and plenty of recharge. These batteries still looked new when
they had to be discarded after only 12 months of service. Because of the
advanced state of memory, recondition was no longer effective to restore
these batteries.
On a further application, I studied the performance of a two-way radio that
was available with batteries of different capacities. It soon was apparent that
the smaller battery lasted much longer, whereas the larger packs needed
replacing more often. The small battery had to work harder and received more
exercise during a daily routine.
Equipment manufacturers are aware of the weak link — the battery. For a
more reliable energy source, higher capacity batteries are recommended. Not
only are oversized batteries bulky, heavy and expensive, they hold more
residual charge prior to recharge than smaller units. If the residual energy is
never fully consumed before a recharge, and no exercise is applied, the
nickel-based battery will eventually lose its ability to hold charge due to
memory.
On the lithium and lead-base systems, a slightly oversized battery offers an
advantage because the pack is less stressed on deep discharges. The battery
does not need to be discharged as low for the given application. A high
residual charge before recharge is a benefit rather than a disadvantage for
these chemistries.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16
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The Correct Battery for the Job
What is the best battery choice? The requirements differ between personal
users and fleet operators. The personal user can choose batteries in various
sizes and chemistries. Cost is a factor for many. If a smaller and less
energy-dense battery is chosen, a spare battery may be carried to assure
continued service.
The energy requirements
are quite different with
fleet operators. The
equipment is matched
with a battery designed
to run for a specified
number of hours per
shift. A degradation
factor to compensate for
battery aging is taken into account. A reserve capacity is added to allow for
unforeseen activities. Allowing an aging degradation factor of 20 percent and
providing a reserve capacity of 20 percent will reduce the usable battery
capacity from 100 percent to 60 percent in a worst-case scenario. Such a
large percentage of reserve capacity may not always be practical but the
equipment manufacturers should consider these safety factors when fitting the
portable devices with a battery.
The best choice is not necessarily an oversized battery, but one that has
sufficient safety margin and is well maintained. This is especially true of
NiCd batteries. When adding large safety margins, the reserve capacity should
be depleted once per month, if this is not done already through normal use.
The NiMH also needs exercising but less often. Cycling lithium-based
batteries is only recommended for the purpose of measuring the performance.
Many battery users have a choice of switching from NiCd to NiMH to obtain
longer runtimes and/or reduce weight. Regulatory bodies advise using less
toxic alternatives because of the environment. But will the NiMH battery
perform as well as the NiCd in industries that require repetitive deep
discharges?
The NiMH will not match the cycle count of the NiCd chemistry. This lower
life expectancy has serious consequences on applications that need one or
several recharges per day. However, in a recent study on battery choice for
heart defibrillators for emergency applications, it was observed that a battery
may cycle far less than anticipated. Instead of the expected 200-cycle count
after two years of use, less than 60 cycles had been delivered. Such service
information is now available with the use of ‘smart’ batteries. With fewer
cycles needed, the switch to lighter and higher energy-dense batteries
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becomes practical for these applications.
In most cases, NiMH can be used as a direct replacement for NiCd. When
doing so, the charger must be checked. A NiMH charger can charge NiCd
batteries, but a charger designed only for the NiCd battery should not be used
to charge NiMH. Battery damage may result due to inaccurate full-charge
detection and excessive trickle charge while in ready mode. If no alternative
exists, the battery should be removed as soon as the green ready light appears.
Battery temperature during charge should also be observed.
Remote control racecar enthusiasts rely heavily on high current capabilities
and quick charging. NiMH batteries are now available that can handle very
high discharge currents. This makes the battery ideally suited for
competitions, because the weight and size of the battery can be reduced.
For most hobbyists, the NiCd remains the preferred choice. The reasons are:
more consistent performance, longer cycle life and lower cost. NiCd needs
replacement less often than NiMH. RC racing experts claim that NiMH is
fragile, temperamental, and can be hurt easily. The storage of the NiMH
battery is also erratic. Some cells are flat after a few weeks of storage; others
still retain a charge.
High load currents have been problematic for NiMH. Discharge currents of
0.5C and higher rob the battery of cycle life. In comparison, NiCd delivers
repetitive high load currents with minimal side effects.
The ultra-high capacity NiCd does not perform as well compared to the
standard version in terms of load characteristics and endurance. Packing more
active material makes the NiCd behave more like a NiMH battery.
The Li-ion battery has limited current handling capabilities. In many cases, it
cannot be used as a replacement for such applications as defibrillators and
power tools, not to mention RC racing. In addition, Li-ion requires a different
charging system than the nickel-based battery chemistries.
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Copyright 2001 Isidor Buchmann. All rights reserved.
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> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
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Battery Analyzers for Critical Missions
Occasionally, a customer will call Cadex because their battery analyzer
appears faulty. The complaint: the battery no longer indicates correct capacity
readings. In most cases, the customer has just purchased new batteries. When
testing these new packs, the capacities read 50 to 70 percent. The customer
assumes that, “Naturally, if two or more of these brand new batteries show
low readings, it can only be the analyzer’s fault.”
Battery analyzers play a critical role in identifying non-performing batteries,
new or old. Conventional wisdom says that a new battery always performs
flawlessly. Yet many users realize that a fresh battery may not always meet
the manufacturer's specifications. Weak batteries can be identified and
primed. If the capacity does not improve, the packs can often be returned to
the vendor for warranty replacement. Whole batches of new batteries have
been sent back because of unacceptable performance. Had these batteries been
released without prior inspection, the whole system would have been
jeopardized, resulting in unpredictable performance and frequent down time.
In addition to getting new batteries field-ready, battery analyzers perform the
important function of weeding out the deadwood in a battery fleet. Weak
batteries can often hide among their peers. However, when the system is put
to the test in an emergency, these non-performers become a real nuisance.
Organizations tend to postpone battery maintenance until a crisis situation
develops. One fire brigade using two-way radios experienced chronic
communication problems, especially during emergency calls which lasted
longer than two hours. Although their radios functioned in the receive mode,
they were not able to transmit and firefighters were left unaware that their
calls did not get through.
The fire brigade acquired a Cadex battery analyzer and all batteries were
serviced through exercise and recondition methods. Those batteries that did
not recover to a preset target capacity were replaced.
Shortly thereafter, the firefighters were summoned to a ten-hour call that
demanded heavy radio traffic. To their astonishment, none of the two-way
radios failed. The success of this flawless operation was credited to the
excellent performance of their batteries. The following day, the Captain of the
fire brigade personally contacted the manufacturer of the battery analyzer and
enthusiastically endorsed the use of the device.
Batteries placed on prolonged standby commonly fail. Such was the case
when a Cadex representative was allowed to view the State Emergency
Management Facility of a large US city. In the fortified underground bunker,
over one thousand batteries were kept in chargers. The green lights glowed,
indicating that the batteries where ready at a moment’s notice. The officer in
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charge stood tall and confidently said, “We are prepared for any emergency”.
The representative then asked the officer to hand over a battery from the
charger to check the state-of-health (SoH). Within seconds, the battery
analyzer detected a fail condition. In an effort to make good, the officer
grabbed another battery from the charger bank but, it failed too. Subsequent
batteries tested also failed.
Scenarios such as these are common but such flaws do not get rectified
quickly. Political hurdles and lack of funding are often to blame. In the
meantime, all the officer can do is pray that no emergency occurs.
Eventually, a new set of batteries is installed and the system returns to full
operational readiness. However, the same scenario will reoccur, unless a
program is implemented to exercise the batteries on a regular basis. Advanced
battery analyzers, such as the Cadex 7000 Series, apply a conditioning
discharge every 30 days to prevent the memory phenomenon on nickel-based
batteries.
Figure 16-1: Results of neglecting your battery’s state-of-health.
Maintenance helps keep deadwood out of your arsenal.
The military also relies heavily on batteries. Defense organizations take great
pride in employing the highest quality and best performing equipment. When
it comes to rechargeable batteries, however, there are exceptions. The battery
often escapes the scrutiny of a full military inspection and only its visual
appearance is checked. Maintenance requirements are frequently ignored.
Little effort is made in keeping track of the battery’s state of health, cycle
count and age. Eventually, weak batteries get mixed with new ones and the
system becomes unreliable. This results in soldiers carrying rocks instead of
batteries. A battery analyzer, when used correctly, keeps deadwood out of the
arsenal.
The task of keeping a battery fleet at an acceptable capacity level has been
simplified with battery analyzers that offer target capacity selection. This
novel feature works on the basis that all batteries must pass a user-defined
performance test. Batteries that fall short are restored with the recondition
cycle. If they fail to recover, the packs are replaced.
The target capacity setting of a battery analyzer can be compared to a student
entry-exam for college. Assuming that the passing mark is 80 percent, the
students who do not obtain that level are given the opportunity to take a
refresher course and are thereafter permitted to rewrite the exam. In our
analogy, the refresher course is the recondition cycle that is applied to
nickel-based batteries. If the passing mark is set to 90 percent, for example,
fewer but higher qualified students are admitted.
A practical target capacity setting for batteries in public safety is 80 percent.
Increasing the capacity requirement to 90 percent will provide an extra
10 percentage points of available energy. However, higher settings will yield
fewer batteries since more packs will fail as they age.
Many organizations allocate the top performing batteries for critical
applications and assign the lower performers for lighter duties. This makes
full use of the available resources without affecting reliability.
Some battery analyzers display both the reserve capacity (motor fuel left in
the tank before refill) and the full-charge capacity (full tank) of the batteries
serviced. The user is then able to calculate how much energy was consumed
during the day by subtracting the reserve from the full-charge capacity. To
ensure a reasonable safety margin after a routine day, the reserve capacity
should be about 20 percent. If less reserve capacity is available, the target
capacity should be set higher. By allowing reasonable reserve capacity,
unexpected downtime in an emergency or on extra-strenuous field activities
can be eliminated.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17
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Chapter 17: Did you know . . .
?
Technological advancements usually take off shortly after a major
breakthrough has occurred. Electricity was discovered circa 1600 AD (or
earlier). At that time, electric power had few other applications than creating
sparks and experimenting with twitching frog legs. Once the relationship with
magnetism was discovered in the mid 1800s, generators were invented that
produced a steady flow of electricity. Motors followed that enabled
mechanical movement and the Edison light bulb was invented to conquer
the dark.
In the early 1900s, the electronic vacuum tube was invented, which enabled
generating and amplifying signals. Soon thereafter broadcasting through the
air by radio waves became possible. The discovery of the transistor in 1947
led to the development of the integrated circuit ten years later. Finally, the
microprocessor ushered in the Information Age and revolutionized the way
we live.
How much has the battery improved during the last 150 years when compared
to other advancements? The progress has been moderate. A battery holds
relatively little power, is bulky, heavy, and has a short life span. Battery
power is also very expensive.
Yet humanity depends on the battery as a power source. In the year 2000, the
total battery energy consumed globally by laptops and mobile phones alone is
estimated to be 2,500MW. This equals 25,000 cars powered by a 100kW
engine (134hp) driving at freeway speed.
Many travelers have experienced the exhilaration of take-off in a jumbo jet.
At a full weight of over 396 tons, the Boeing 747 requires 90MW of energy to
get airborne. The global battery power consumed by mobile phones and
laptops could simultaneously lift off 28 jumbo jets. The energy consumption
while cruising at high altitude is reduced to about half, or 45MW. The
batteries that power our mobile phones and laptops could keep 56 Boeing
747s in the air.
The mighty Queen Mary, an 81,000 ton cruise ship measuring over 300 m
(1000 ft) in length, was propelled by four steam turbine engines producing a
total of 160,000hp. The energy consumed globally by mobile phones and
laptops could power 20 Queen Mary ships, with 3000 passengers and crew
aboard, traveling at a speed of 28.5 knots (52 km/hr). The Queen Mary was
launched in 1934 and is now retired in Long Beach, California.
In this concluding chapter, we compare the cost of battery power against
energy created by the combustion engine and the emerging fuel cell. We also
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examine the cost of electricity delivered through the electric utility system.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17
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The Cost of Mobile Power
Among the common power sources, energy from non-rechargeable batteries is
the most expensive. Figure 17-1 reflects the cost per kWh using
non-rechargeable batteries, also referred to as primary batteries. In addition,
non-rechargeable batteries have a high internal cell resistance, which limits
their use to light loads with low discharge currents.
In the last few decades, there has been a shift from non-rechargeable to
rechargeable batteries, also known as secondary batteries. The convenience of
recharging, low cost and reliable operation have contributed to this. Another
reason for the increased popularity of the secondary battery is the larger
energy densities available. Some of the newer rechargeable lithium systems
now approach or exceed the energy density of a primary battery.
AAA Cell
AA Cell
C Cell
D Cell
Capacity
(alkaline)
1100mAh
2500mAh
7100mAh
14,300mAh 600mAh
Energy
(single cell)
1.4Wh
3Wh
9Wh
18Wh
4.2Wh
Cost per
Cell (US$)
$1.25
$1.00
$1.60
$1.60
$3.10
Cost per
$890
KWh (US$)
$330
$180
$90
$730
9 Volt
Figure 17-1: Energy and cost comparison of primary alkaline cells.
Energy from primary batteries is most expensive. The cost increases with
smaller battery sizes.
Figure 17-2 compares the cost of power when using rechargeable batteries.
The analysis is based on the purchase cost of the battery and the number of
discharge-charge cycles it can endure before replacement is necessary. The
cost does not include the electricity needed for charging, nor does it account
for the cost of purchasing and maintaining the charging equipment.
Capacity
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NiCd
NiMH
AA Cell AA Cell
Lead Acid Li-ion
Reusable
(typical
18650 Cell Alkaline
pack)
AA Cell
600mAh 1000mAh
2000mAh
1200mAh
1400mAh 1
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Battery
Voltage
7.5V
7.5V
12V
7.2V
7.5V
Energy per
cycle
4.5Wh
7.5Wh
24Wh
8.6Wh
6.3Wh
Cycle life
1500
500
250
500
10
Cost per
$50
battery (ref.
only)
$70
$50
$100
$6.00
Cost per
kWh ($US)
$18.50
$8.50
$24.00
$95.00
$7.50
Figure 17-2: Energy and cost comparison using rechargeable cells.
Older battery technologies offer lower energy costs compared to new systems.
In addition, larger cells are more cost-effective than small cells. The battery
packs taken for comparison are for commercial applications at
over-the-counter prices.
For this calculation, 840mA is used since subsequent capacities are rated at
840mA (60% of initial capacity). If the battery is discharged partially, a
higher cycle life can be obtained.
Figure 17-3 evaluates the cost to generate 1kW of energy. We take into
account the initial investment, add the fuel consumption and include the
eventual replacement of each system.
Power obtained through the electrical utility grid is most cost effective.
Consumers in industrialized countries pay between $0.05 and 0.15US
per kWh. The typical daily energy consumption of a household is 25kWh.
Investment
of equipment to
generate 1kW
Lifespan
Cost of
of equipment fuel
before major per kWh
overhaul or
replacement
Total Cost
per kWh, incl.
fuel,
maintenance
and equipment
replacement
NiCd
for portable
use
$7,000, based on 1500 h,
$0.15 for $7.50
7.2V, 1000mAh at based on 1C electricity
$50/pack
discharge
Gasoline
Engine for
mobile use
$30, based on
$3,000/100kW
(134hp)
4000 h
$0.10
$0.14
Diesel
$40, based on
Engine
$4,000/100kW
for stationary (134hp)
use
5000 h
$0.07
$0.10
Fuel Cell
$3,000 – 7,500
$0.35
- for portable
use
2000 h
-->
$1.85 – 4.10
- for mobile
use
4000 h
-->
$1.10 – 2.25
- for
stationary use
40,000 h
-->
$0.45 – 0.55
Electricity
from electric
grid
All inclusive
All inclusive $0.10
$0.10
Figure 17-3: Cost of generating 1kW of energy.
This takes into account the initial investment, fuel consumption, maintenance
and eventual replacement of the equipment. The most economical power
source is by far the utility; the most expensive is portable batteries.
The fuel cell offers the most effective means of generating electricity, but is
expensive in terms of cost per kWh. This high cost is made economical when
comparing with portable rechargeable batteries. For mobile and stationary
applications, the fuel cell is considerably more expensive than conventional
methods.
Note: The costing information obtained on the fuel cell is based on current
estimates and assumptions. It is anticipated that improvements and wider use
of this technology will eventually lower the cost to be competitive with
conventional methods.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17
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The Fuel Cell
A fuel cell is an electrochemical device which combines hydrogen fuel with
oxygen to produce electric power, heat and water. In many ways, the fuel cell
resembles a battery. Rather than applying a periodic recharge, a continuous
supply of oxygen and hydrogen is supplied from the outside. Oxygen is drawn
from the air and hydrogen is carried as a fuel in a pressurized container. As
alternative fuel, methanol, propane, butane and natural gas can be used.
The fuel cell does not generate energy through burning; rather, it is based on
an electrochemical
process. There are little
or no harmful emissions.
The only release is clean
water. In fact, the water
is so pure that visitors to
Vancouver’s Ballard
Power Systems, the
leader in the
development of the proton exchange membrane fuel cell (PEMFC), drank
clear water emitted from the tailpipes of buses powered by a Ballard fuel cell.
The fuel cell is twice as efficient in converting fuel to energy through a
chemical process than combustion. Hydrogen, the simplest element consisting
of one proton and one electron, is plentiful and is exceptionally clean as a
fuel. Hydrogen makes up 90 percent of the composition of the universe and is
the third most abundant element on the earth’s surface. Such a wealth of fuel
would provide an almost unlimited pool of energy at relatively low cost. But
there is a price to pay. The fuel cell core (or ‘stack’), which converts oxygen
and hydrogen to electricity, is expensive to build.
Hydrogen must be carried in a pressurized bottle. If propane, natural gas or
diesel are used, a reformer is needed to convert the fuel to hydrogen.
Reformers for PEMFCs are bulky and expensive. They start slowly and
purification is required. Often the hydrogen is delivered at low pressure and
additional compression is required. Some fuel efficiency is lost and a certain
amount of pollution is produced. However, these pollutants are typically
90 percent less than what comes from the tailpipe of a car.
The fuel cell concept was developed in 1839 by Sir William Grove, a Welsh
judge and gentleman scientist. The invention never took off, partly because of
the success of the internal combustion engine. It was not until the second half
of the 20th century when scientists learned how to better utilize materials such
as platinum and TeflonÔ, that the fuel cell could be put to practical use.
A fuel cell is electrolysis in reverse, using two electrodes separated by an
electrolyte. Hydrogen is presented to the negative electrode (anode) and
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oxygen to the positive electrode (cathode). A catalyst at the anode separates
the hydrogen into positively charged hydrogen ions and electrons. On the
PEMFC system, the oxygen is ionized and migrates across the electrolyte to
the anodic compartment where it combines with hydrogen. The byproduct is
electricity, some heat and water. A single fuel cell produces 0.6 to 0.8V under
load. Several cells are connected in series to obtain higher voltages.
The first practical application of the fuel cell system was made in the 1960s
during the Gemini space program, when this power source was favored over
nuclear or solar power. The fuel cell, based on the alkaline system, generated
electricity and produced the astronauts’ drinking water. Commercial
application of this power source was prohibitive because of the high cost of
materials. In the early 1990s, improvements were made in stack design, which
led to increased power densities and reduced platinum loadings at the
electrodes.
High cost did not hinder Dr. Karl Kordesch, the co-inventor of the alkaline
battery, from converting his car to an alkaline fuel cell in the early 1970s.
Dr. Kordesch drove the car for many years in Ohio, USA. The hydrogen tank
was placed on the roof and the trunk was utilized to store the fuel cell and
back-up batteries. According to Dr. Kordesch, there was “enough room for
four people and a dog”.
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Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
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Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
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Types of fuel cells — Several variations of fuel cell systems have emerged.
The most common are the previously mentioned and most widely developed
PEMFC systems using a polymer electrolyte. This system is aimed at vehicles
and portable electronics. Several developers are also targeting stationary
applications. The alkaline system, which uses a liquid electrolyte, is the
preferred fuel cell for aerospace applications, including the space shuttle.
Molten carbonate, phosphoric acid and solid oxide fuel cells are reserved for
stationary applications, such as power generating plants for electric utilities.
Among these stationary systems, the solid oxide fuel cell system is the least
developed but has received renewed attention due to breakthroughs in cell
material and stack designs.
The PEMFC system allows compact designs and achieves a high energy to
weight ratio. Another advantage is a quick start-up when hydrogen is applied.
The stack runs at a low temperature of about 80°C (176°F). The efficiency is
about 50 percent (in comparison, the internal compaction motor has an
efficiency of about 15 percent).
The limitations of the PEMFC system are high manufacturing costs and
complex water management issues. The stack contains hydrogen, oxygen and
water. If dry, the input resistance is high and water must be added to get the
system going. Too much water causes flooding.
The PEMFC has a limited temperature range. Freezing water can damage the
stack. Heating elements are needed to keep the fuel cell within an acceptable
temperature range. The warm-up is slow and the performance is poor when
cold. Heat is also a concern if the temperature rises too high.
The PEMFC requires heavy accessories. Operating compressors, pumps and
other apparatus consumes 30 percent of the energy generated. The PEMFC
stack has an estimated service life of 4000 hours if operated in a vehicle. The
relatively short life span is caused by intermittent operation. Start and stop
conditions induce drying and wetting, which contribute to membrane stress. If
run continuously, the stationary stack is good for about 40,000 hours. The
replacement of the stack is a major expense.
Type of
Fuel Cell
Applications Advantages
Limitations
Status
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Proton
Exchange
Membrane
(PEMFC)
Mobile
(buses, cars),
portable
power,
medium to
large-scale
stationary
power
generation
(homes,
industry).
Compact
design;
relatively long
operating life;
adapted by
major
automakers;
offers quick
start-up, low
temperature
operation,
operates at
50%
efficiency.
High
manufacturing
costs, needs
heavy
auxiliary
equipment
and pure
hydrogen, no
tolerance for
contaminates;
complex heat
and water
management.
Most widely
developed;
limited
production; offers
promising
technology.
Alkaline
(AFC)
Space
(NASA),
terrestrial
transport
(German
submarines).
Low
manufacturing
and operation
costs; does not
need heavy
compressor,
fast cathode
kinetics.
Large size;
needs pure
hydrogen and
oxygen; use
of corrosive
liquid
electrolyte.
First generation
technology, has
renewed interest
due to low
operating costs.
Molten
Large-scale
Carbonate power
(MCFC)
generation.
Highly
efficient;
utilizes heat to
run turbines
for
co-generation.
Electrolyte
instability;
limited
service life.
Well developed;
semi-commercial.
Phosphoric Medium to
Acid
large-scale
(PAFC)
power
generation.
Commercially
available;
lenient to
fuels; utilizes
heat for
co-generation.
Low
efficiency,
limited
service life,
expensive
catalyst.
Mature but faces
competition from
PEMFC.
Solid
Oxide
(SOFC)
High
efficiency,
lenient to
fuels, takes
natural gas
directly, no
reformer
needed.
Operates at
60%
efficiency;
utilizes heat
for
co-generation.
High
operating
temperature;
requires
exotic metals,
high
manufacturing
costs,
oxidation
issues; low
specific
power.
Least developed.
Breakthroughs in
cell material and
stack design sets
off new research.
Medium to
large-scale
power
generation.
Direct
Methanol
(DMFC)
Suitable for
portable,
mobile and
stationary
applications.
Compact
design, no
compressor or
humidification
needed; feeds
directly off
methanol in
liquid form.
Complex
stack
structure,
slow load
response
times;
operates at
20%
efficiency.
Laboratory
prototypes.
Figure 17-4: Advantages and disadvantages of various fuel cell systems.
The PEMFC is the most widely developed system.
Figure 17-5: 1kW portable fuel cell generator.
The unit is a fully automated power system, which converts hydrogen fuel and
oxygen from air directly into DC electricity. Water is the only by-product of
the reaction. This fuel cell generator, which operates at low pressures,
provides reliable, clean, quiet and efficient power. It is small enough to be
carried to wherever power is needed. Illustration courtesy of Ballard Power
Systems Inc., February 2001.
The SOFC is best suited for stationary applications. The system requires high
operating temperatures (about 1000°C). Newer systems are being developed
which can run at about 700°C.
A significant advantage of the SOFC is its leniency on fuel. Due to the high
operating temperature, hydrogen is produced through a catalytic reforming
process. This eliminates the need for an external reformer to generate
hydrogen. Carbon monoxide, a contaminant in the PEMFC system, is a fuel
for the SOFC. In addition, the SOFC system offers a fuel efficiency of
60 percent, one of the highest among fuel cells. The 60 percent efficiency is
achieved with co-generation, meaning that the heat is utilized.
Higher stack temperatures add to the manufacturing cost because they require
specialized and exotic materials. Heat also presents a challenge for longevity
and reliability because of increased material oxidation and stress. High
temperatures, however, can be utilized for co-generation by running steam
generators. This improves the overall efficiency of this fuel cell system.
The AFC has received renewed interest because of low operating costs.
Although larger in physical size than the PEMFC system, the alkaline fuel cell
has the potential of lower manufacturing and operating costs. The water
management is simpler, no compressor is usually needed, and the hardware is
cheaper. Whereas the separator for the PEMFC stack costs between $800 and
$1,100US per square meter; the equivalent of the alkaline system is almost
negligible. (In comparison, the separator of a lead acid battery is $5 per square
meter.) As a negative, the alkaline fuel cell needs pure oxygen and hydrogen
to operate. The amount of carbon dioxide in the air can poison the alkaline
fuel cell.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17
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Applications — The fuel cell is being considered as an eventual replacement
for the internal combustion engine for cars, trucks and buses. Major car
manufacturers have teamed up with fuel cell research centers or are doing
their own development. There are plans for mass-producing cars running on
fuel cells. However, because of the low operating cost of the combustion
engine, and some unresolved technical challenges of the fuel cell, experts
predict that a large scale implementation of the fuel cell to power cars will not
occur before 2015, or even 2020.
Large power plants running in the 40,000kW range will likely out-pace the
automotive industry. Such systems could provide electricity to remote
locations within 10 years. Many of these regions have an abundance of fossil
fuel that could be utilized. The stack on these large power plants would last
longer than in mobile applications because of steady use, even operating
temperatures and absence of shock and vibration.
Residential power supplies are also being tested. Such a unit would sit in the
basement or outside the house, similar to an air-conditioning unit of a typical
middle class North American home. The fuel would be natural gas or
propane, a commodity that is available in many urban settings.
Fuel cells may soon compete with batteries for portable applications, such as
laptop computers and mobile phones. However, today’s technologies have
limitations in meeting the cost and size criteria for small portable devices. In
addition, the cost per watt-hour is less favorable for small systems than large
installations.
Let’s examine once more the cost to produce 1kW of power. In Figure 17-5
we learned that the investment to provide 1kW of power using rechargeable
batteries is around $7,000. This calculation is based on 7.2V; 1000mAh NiCd
packs costing $50 each. High energy-dense batteries that deliver fewer cycles
and are more expensive than the NiCd will double the cost.
The high cost of portable power opens vast opportunities for the portable fuel
cell. At an investment of $3,000 to $7,500 to produce one kilowatt of power,
however, the energy generated by the fuel cell is only marginally less
expensive than that produced by conventional batteries.
The DMFC, the fuel cell designed for portable applications would not
necessarily replace the battery in the equipment but serve as a charger that is
carried separately. The feasibility to build a mass-produced fuel cell that fits
into the form factor of a battery is still a few years away.
The advantages of the portable fuel
cell are: relatively high energy
density (up to five times that of a
Li-ion battery), liquefied fuel as
energy supply, environmentally
clean, fast recharge and long
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runtimes. In fact, continuous
operation is feasible. Miniature
fuel cells have been demonstrated that operate at an efficiency of 20 percent
and run for 3000 hours before a stack replacement is necessary. There is,
however, some degradation during the service life of the fuel cell. Portable
fuels cells are still in experimental stages.
Advantages and limitations of the fuel cell — A less known limitation of
the fuel cell is the marginal loading characteristic. On a high current load,
mass transport limitations come into effect. Supplying air instead of pure
oxygen aggregates this phenomenon.
The issue of mass transport limitation is why the fuel cell operates best at a
30 percent load factor. Higher loads reduce the efficiency considerably. In
terms of loading characteristics, the fuel cell does not match the performance
of a NiCd battery or a diesel engine, which perform well at a 100 percent load
factor.
Ironically, the fuel cell does not eliminate the chemical battery — it promotes
it. Similar to the argument that the computer would make paper redundant, the
fuel cell needs batteries as a buffer. For many applications, a battery bank will
provide momentary high current loads and the fuel cell will serve to keep the
battery fully charged. For portable applications, a supercapacitor will improve
the loading characteristics and enable high current pulses.
Most fuel cells are still
handmade and are used for
experimental purposes.
Fuel cell promoters remind
the public that the cost will
come down once the cells
are mass-produced. While
an internal combustion
engine requires an investment of $35 to $50 to produce one kilowatt of power,
the equivalent cost in a fuel cells is still a whopping $3,000 to $7,500. The
goal is a fuel cell that would cost the same or less than diesel engines.
The fuel cell will find applications that lie beyond the reach of the internal
combustion engine. Once low cost manufacturing is feasible, this power
source will transform the world and bring great wealth potential to those who
invest in this technology.
It is said that the fuel cell is as revolutionary in transforming our technology
as the microprocessor has been. Once fuel cell technology has matured and is
in common use, our quality of life will improve and the environmental
degradation caused by burning fossil fuels will be reversed. However, the
maturing process of the fuel cell may not be as rapid as that of
microelectronics.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17
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The Electric Vehicle
In a bid to lower air pollution in big cities, much emphasis has been placed on
the electric car. The notion of driving a clean, quiet and light vehicle appeals
to many city dwellers. Being able to charge the car at home for only a dollar a
day and escape heavy fuel taxes (at least for the time being) makes the electric
car even more attractive.
The battery is still the main challenge in the development of the electric car.
Distance traveled between recharge, charge time and the limited cycle count
of the battery continue to pose major concerns. Unless the cycle life of the
battery can be increased significantly, the cost per mile will be substantially
higher than that of a fuel-powered vehicle. The added expense is the need to
replace the battery after a given number of recharges. This could offset any
advantage of lower energy costs or the absence of fuel taxes. Disposing the
spent batteries also adds to the expenditure.
Another challenge associated with the electric vehicle is the high power
demand that would be placed on the electric grid if too many cars were
charged at a certain time. Each recharge consumes between 15 to 20kW of
power, an amount that is almost as much as the daily power requirement of a
smaller household. By adding one electric car per family, the amount of
electric power a residence requires would almost double. Delayed charging
could ease this problem by only drawing power during the night when the
consumption is low.
A rapid shift to the electric car could create shortages of electric power. With
the move to reduce the generation of electricity due environmental concerns,
electricity would need to be imported at high costs. This would make the
electric car less attractive.
If the electricity was generated with renewable energy such as hydroelectric
generators and windmills, the electric vehicle would truly clear the air in big
cities. The generation of electricity by means of nuclear power or fossil fuels
simply shifts the pollution problem elsewhere. However, a central source of
pollution is easier to contain than many polluting objects in a
metropolitan area.
A hybrid car is an alternative to vehicles running solely on battery power.
Here, a small combustion engine works in unison with an electric motor.
During acceleration, both the electric and combustion engines are engaged.
Because of superior torque, the electric motor takes precedence during
acceleration. Once cruising, the combustion engine maintains the speed and
keeps the batteries charged. Hybrid cars achieve fuel savings of 30 percent or
better compared to the combustion engine alone.
A hybrid car is less strenuous on a battery than a conventional electric car
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because the battery is not being deeply discharged during regular use. A deep
discharge only occurs on a long mountain climb where the small combustion
engine could not sustain the load and would need assistance from the electric
motor and its battery bank. Driving habits would, to a large extent, determine
the service life of the battery. A light foot on the pedal will help the pocket
book also with the hybrid car.
Another alternative to powering cars is the fuel cell. Although much cleaner
running than the combustion engine, the fuel cell must solve a number of
critical problems before the product can be offered to the consumer as an
economical alternative. The major challenge is cost reduction. If fossil fuel
remains as low-priced is it is today, many drivers owning high-powered cars,
SUVs and trucks would be reluctant to switch to a new technology. Concerns
over pollution only persuade a limited number of drivers to switch to a
cleaner-running vehicle. With the slow and gradual progress in the fuel cell, it
will be some time before this technology renders the combustion engine
obsolete.
Europe is talking about the three-liter motor, an internal combustion engine
running on gasoline or diesel fuel. Remarkably, ‘three’ does not denote the
engine displacement but stands for liters of fuel consumed per 100 km
traveled. There is talk about the one-liter engine also. Major car
manufacturers are divided on the fuel that will power our cars in the future.
Within one large auto manufacturer in Europe, opinions regarding the fuel
cell and an economical three-liter engine are divided fifty-fifty.
Strengthening the Weakest Link
The speed at which mobility can advance hinges much on the battery. So
important is this portable energy that engineers design handheld devices
around the battery, rather than the other way around. With each incremental
improvement of the battery, the doors swing open for new products and
applications. It is the virtue of the battery that provides us the freedom to
move around and stay in touch. The better the battery, the greater the freedom
we can enjoy.
The longer runtime of newer
portable devices is not only
credited to higher energy-dense
batteries. Much improvement has
been made in reducing the power
consumption of portable
equipment. These advancements
are, however, counteracted with
the demand for more features and
faster processing time. In mobile computing, for example, high speed CPUs,
large screens and wireless interface are a prerequisite. These features eat up
the reserve energy that the more efficient circuits save and the improved
battery provides. The result is similar runtime to an older system, but with
increased performance. It is predicted that the improvements in battery
technology will keep par with better performance.
Wide-band mobile phones, dubbed G3 for third generation, are being offered
as replacements for the digital voice phone. There is public demand for
Internet access in a tiny handset that connects to the world by the push of a
few buttons, twenty-four hours a day. But these devices require many times
the power compared to voice only when operating on wideband. Higher
capacity batteries are needed, preferably without added size and weight. In
fact, the success of the G3 system could hinge on the future performance of
the battery. G3 technology may be ready but the battery lags behind.
The battery has not leap-frogged at the same speed as microelectronics. Only
5 to 10 percent gains in capacity per year have been achieved during the last
decades and the ultimate miracle battery is still nowhere in sight. As long as
the battery is based on an electro-chemical process, limitations of power
density and life expectancy must be taken into account.
The battery remains the ‘weak link’ for the foreseeable future. A radical turn
will be needed to satisfy the unquenchable thirst for mobile power. What
people want is an inexhaustible pool of energy in a small package. It is
anyone’s guess whether the electro-chemical battery of the future, the fuel cell
or some groundbreaking new energy storage device will fulfill this dream.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17 > Part 4
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invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17 > Part 4 >
Chapter 18
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Chapter 18: Beginnings and
Horizons
About the Author
A versatile inventor, researcher and writer, Mr. Isidor Buchmann is the
president, founder and CEO of Cadex Electronics Inc., located in Richmond
(Vancouver), Canada.
Fascinated by electronics during his high school years, Mr. Buchmann took to
inventing at an early age, designing a fuel-powered engine that was based on
continuous combustion. His drawings and theory of operation were reviewed
by Felix Wankel, inventor of the Wankel Rotary Engine, who kindly replied
that while the design was indeed unique and original, manufacturing would be
too expensive to be commercially viable. Further to his credit, Mr. Buchmann
invented a broadcast radio that ran on no power — it required only an antenna
and a ground connection (it didn’t even use a battery). Mr. Buchmann sold
several of these radio receivers to his family and colleagues and later set up a
workshop in the attic where he restored and resold old radios. After high
school, a four-year apprenticeship as a Radio Technician brought him
practical experience in a workshop environment as well as academic theory.
Finally, his experience with radio communications in the Swiss army led to
his decision to make electronics his life's work.
Realizing that conservative Switzerland would not satisfy his entrepreneurial
spirit, Mr. Buchmann emigrated to Canada in 1966, eventually finding
employment in the radio communications department at General Electric.
There he realized that a major problem with two-way radios was the battery's
short life and, as part of his job, tested a wide variety of customer batteries
that came in. In his spare time at home, he continued to research and develop
electronic devices in his spare time, developing a battery analyzer that
featured a ‘recondition’ program which restored weakened nickel cadmium
batteries.
To prevent a conflict of interest with his employer, Mr. Buchmann quit his job
with GE and started Cadex. The first battery analyzer, the Cadex 450, was
introduced in 1981 but failed to achieve the anticipated market acceptance.
Still in his spare time, Mr. Buchmann designed the modular Cadex 550
battery analyzer. This model sold reasonably well at first but it soon became
evident that manufacturing methods needed to be improved to make it cost
effective.
In 1984, Cadex moved from a small room in Mr. Buchmann's residence to
rented facilities. With increased overhead costs, a staff to maintain and
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sluggish sales, cash flow became tight. Bank loans for start-up companies,
especially high-tech firms, were almost non-existent at the time, so Mr.
Buchmann worked from home during the day looking after his growing
children and spent time in the office during the evening. Happily, the
company survived the slump and managed to add a number of new products.
Profitability returned and the staff grew.
Knowing that the wealth of an organization is in human resources, Isidor
resolved to provide an environment that was conducive to attracting good
people with skills that complemented his own strengths and weaknesses.
Spacious new headquarters in a park-like setting overlooking the scenic
Fraser River add to a pleasant working experience. Under Mr. Buchmann’s
leadership, new and innovative products were developed that generated rapid
growth and created global recognition of Cadex.
Today, Cadex is a world leader in the design and manufacture of battery
analyzers and chargers.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17 > Part 4 >
Chapter 18
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About Cadex
Cadex Electronics Inc. was established in 1980 in Vancouver, Canada.
Isidor Buchmann, founder, president and CEO recognized that the full
potential of nickel cadmium batteries was not being achieved and developed a
battery analyzer to exercise and rejuvenate them.
In its early days, the company operated under the name Buchmann
Enterprises Inc. Until 1983, all activities were conducted in a small room of
the founder’s residence. In 1985, after the registered trademark for the name
‘Cadex’ was granted, the company changed the corporate name to Cadex
Electronics Inc. Cadex is derived from ‘CADmium-EXerciser.’
The first product, the Cadex 450, entered the market in 1981. Only a few units
sold. Mr. Buchmann then designed a modular battery analyzer that was able
to service three batteries simultaneously, with expansion to ten. Called the
Cadex 550, this unit sold reasonably well and became the workhorse for many
two-way radio users, such as railways, public safety and oil companies.
The Government of Canada awarded Cadex funds to develop a new
generation of battery analyzers and in 1988 the Cadex 6000 was launched.
This new product was capable of servicing up to 64 batteries unattended. A
private company then commissioned Cadex to develop and manufacture an
intelligent fast-charger for the End-of-Train Unit, a device that replaced the
caboose on a freight train. This charger was later expanded into a four-station
battery analyzer called Cadex 2000. Packaged into a compact desktop
housing, the Cadex 2000 provided a low cost alternative to the modular
Cadex 6000 system.
Towards the end of the 1980s, batteries began to diversify and it became
evident that a battery analyzer needed to adapt to a large pool of different
battery models. With the help of the Science Council of British Columbia and
the National Research Council of Canada, Cadex designed an open platform
battery analyzer that was software driven similar to a PC. In 1991, the first
user-programmable battery analyzer was introduced. Called the Cadex 4000
for its four independent stations, this instrument immediately gained the
interest of many battery users, both in North America and overseas. Some of
the main features were the interchangeable battery adapters that contained a
memory chip holding the unique battery configuration code, ‘C-code’ in
short. With a few key stokes, the user was able to program and reprogram the
analyzer to fit virtually any battery type.
In 1992, as part of a five-year program for a US defense project, Racal
Communications commissioned Cadex to build intelligent fast-chargers and
battery reconditioners. During this partnership, Cadex was the recipient of
several Racal awards. The Supplier Recognition Award for Outstanding
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Performance, which Cadex received on two separate occasions, was granted
to only six of over one thousand suppliers.
In 1995, Cadex introduced the Cadex 7000 Series, an upgraded version of the
Cadex 4000 battery analyzer. The Cadex SnapLock adapters allowed quick
and convenient changes from one battery type to another. The Cadex 7000
Series analyzer became the company’s flagship and established a new global
standard to which competitive products were compared.
In 1996, an agreement was reached with Medtronics, (then Physio Control
Corporation) to design and supply intelligent battery chargers/ conditioners as
part of a five-year contract. In the same year, Cadex received the British
Columbia Export Award for outstanding achievements in export.
In 1997, Cadex published the book Batteries in a Portable World — A
Handbook on Rechargeable Batteries for Non-Engineers. Many of
Mr. Buchmann’s articles on battery technology also gained recognition by
appearing in leading trade magazines. By then, Cadex had achieved
international market recognition with a customer base of over 100 countries.
In 1998, Motorola and Cadex engaged in a partnership to manufacture battery
analyzers for distribution through Motorola’s global network. In the same
year, Mr. Buchmann was selected as a finalist in the Entrepreneur of the Year
program.
In 1999, Cadex received ISO 9001 certification. The company moved to the
custom built headquarters in Fraserwood Industrial Park, Richmond, British
Columbia, a suburb of Vancouver. In the same year, Cadex Batteryshop™
was released. This high level software integrates the Cadex 7000 Series
battery analyzers with a PC to bring battery testing and maintenance within
the reach of the untrained user. The task of entering battery parameters was
reduced to either scanning a bar code label or the ‘point and click’ of the
mouse.
In the same year, Cadex released the SM1 and SM2+ intelligent battery
chargers. The Cadex SM2+ charger features a target capacity selector that
passes or fails a battery based on state-of-health (SoH). If low, the user is
prompted to restore the battery by pressing the condition key. Today, these
chargers service batteries for mobile computing, medical instrumentation and
survey equipment.
In the year 2000, Cadex developed Quicktest™, a technique that checks the
SoH of a battery in three minutes. The system works on a neuro-logic network
based on fuzzy logic, is self-learning and adapts to new chemical
combinations as introduced from time to time.
During the year 2001, Cadex will introduce a new generation of 7000 Series
battery analyzers. A two-station Cadex 7200 has been added to serve smaller
battery users. Retaining the powerful priming and reconditioning features of
the previous models, the emphasis is moving towards quick testing, boosting
and ultra-fast charging of batteries. These services take only minutes and can
restore a battery on the run.
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Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17 > Part 4 >
Chapter 18
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Working with Natural Beauty
The new Cadex headquarters is nestled in natural surroundings. The scenic
Fraser River lies to the south, a public park to the east and the Coastal
Mountains to the north. For joggers and cyclists, there is a nature path
between the building and the river.
The interior of the building is designed with employee comfort in mind. It
includes a snooker table, a gym, shower rooms, and several televisions.
Balconies with a river view overlook the outdoor patio, which is used for
summer lunches.
With the wonders of nature at its door, Cadex offers its staff a tranquil
alternative to the noise and hustle of crowded city streets. And yet, the
location is within easy reach of Vancouver’s downtown, is central to the
surrounding suburban areas and is close to Vancouver International Airport.
Figure 18-1: Cadex headquarters in Richmond, Canada.
With the wonders of nature at its door, Cadex offers its staff a tranquil
alternative to the noise and hustle of crowded city streets.
Customer Comments
A manager who is in charge of manufacturing and warranties for a large
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mobile phone provider writes: “I feel that by having the ability to analyze and
condition our customer’s batteries, we have also increased our battery sales.
We now recommend that all customers stop by and allow us to condition their
batteries at least once every six months. Many customers will buy another
battery to use while their pack is being conditioned. The customers feel that
the maintenance program enables them to achieve longer battery life.
Providing battery conditioning service has helped us increase customer
loyalty and satisfaction, which in turn helps our bottom line in this
competitive industry.”
When setting up a battery refurbishing service, the quality of battery analyzers
is of importance. A manager in charge of battery warranty with a leading
mobile phone manufacturer commented: “With the Cadex 7000 Series
analyzers, our team was able to achieve a 90 percent recovery rate for all
warranty batteries, compared to just 60 percent before the Cadex analyzers
were brought on stream. The savings were absolutely immense.”
Another Regional Service Manager for a mobile phone provider wrote: “The
recovery rate of batteries has been far better than expected. We used to run
them on our old equipment and if they failed we would then run them on the
Cadex. Over 50 percent of the batteries would pass our target capacity of
80 percent. That in itself saved us a tremendous amount of expense. It enables
us to return the batteries to the customer for further use.”
These above mentioned reports are mostly based on servicing nickel-based
batteries. The recovery rate is expected to be lower with the Li-ion batteries,
which are considered maintenance free. But to everyone’s amazement,
lithium-based batteries enjoy a similar recovery rate, especially in the mobile
phone market. Here, the cause of failure is not memory-based, especially
during the warranty period. Lack of customer preparation and failure to
understand the behavior of a battery as a portable energy source may be to
blame. The true reason for the failures may never be known.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery invented? >
Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance or hype? >
Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last > Article:
Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies > Article:
Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement > Article: The Fuel
Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 > Chapter 8 > Chapter 9 >
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Cadex Products
Cadex products are built with one goal in mind — to make batteries run longer.
Cadex has realized the importance of battery care and is offering equipment to
charge, test, monitor, and restore batteries.
Cadex’s core competence is engineering. Over 25 percent of the Cadex staff is
active in the Engineering Department. Existing products are improved on a
continual basis, and new and creative products are added to adjust to the changing
demands of battery users. Key products include:
Figure 18-2: Cadex 7200 battery analyzer.
This compact two-station battery analyzer brings battery maintenance within
reach of all battery users.
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18-3: Cadex 7400 battery analyzer.
Provision to service four batteries simultaneously increases the service
throughput. The Cadex 7400 offers parallel printer port and USP for easy
interface to a PC.
Cadex 7000 Series battery analyzers solve the common battery problems of
uncertain service and short life. Pre-configured ‘Snap Lock’ adapters enable
quick interface with all major batteries for wireless communications devices,
laptops, biomedical equipment, video cameras and other portable devices.
Irregular batteries connect by universal cables that can be programmed with the
analyzer’s menu function. The analyzer supports Li-ion/Polymer, NiMH, NiCd
and Sealed Lead Acid (SLA) batteries.
The Cadex 7000 Series features the self-learning Cadex Quicktest™ program that
performs an in-depth battery diagnosis in three minutes. Other programs include:
‘Boost’ to wake up low voltage batteries; ‘Auto’ to recondition weak batteries and
‘Prime’ to format new batteries. In addition, ‘Self-Discharge’ verifies charge
retention; ‘CycleLife’ tests longevity and ‘Custom’ enables user-defined
programs. The Cadex 7200 services two batteries simultaneously; the Cadex 7400
accommodates four.
The battery voltage is programmable from 1.2 to 15V with a current range of
100mA to 24A. If set high, the analyzer automatically reduces the current to
remain within the 4A per station handling capabilities. With a printer, service
reports and battery labels can be generated. The unit operates as stand-alone or
with a PC.
Figure 18-4: Cadex Batteryshop™.
This Windows-based software allows untrained users to perform accurate and
expedient battery tests. With the same system, a design engineer can collect
valuable battery information running customized test programs.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
Home > Site Map > Advanced Search > Search Tips > FAQ > New Articles > About the Author > Order Book > Links > Article: When was the battery
invented? > Article: What is the perfect battery? > Article: Will Lithium-Ion batteries power the new millennium? > Article: The Li-Polymer battery: substance
or hype? > Article: Can the Lead Acid battery compete in modern times? > Article: The Secrets of Battery Runtime > Article: Choosing a battery that will last
> Article: Memory, myth or fact? > Article: The battery and the digital load > Article: Is the ‘smart’ battery help or deterrent? > Article: The 'Green Light' Lies
> Article: Battery testers for modern batteries > Article: Breakthrough in battery quick testing > Article: Caring for your Batteries from Birth to Retirement >
Article: The Fuel Cell, Is it Ready? > Article: Recycling your Battery > Chapter 2 > Chapter 3 > Chapter 4 > Chapter 5 > Part 2 > Chapter 6 > Chapter 7 >
Chapter 8 > Chapter 9 > Chapter 10 > Chapter 11 > Chapter 12 > Chapter 13 > Part 3 > Chapter 14 > Chapter 15 > Chapter 16 > Chapter 17 > Part 4 >
Chapter 18
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Cadex Batteryshop™ software provides a simple, yet powerful PC interface
to control and monitor the Cadex 7000 Series battery analyzers. Running on
Windows 95, 98 and NT, the software enables untrained staff to test batteries
as part of customer service. In addition, Cadex Batteryshop™ schedules
periodic maintenance for fleet owners and assists battery manufacturers with
quality control.
Cadex Batteryshop™ includes a database of over 2000 common battery
models. Each battery listing contains the configuration code (C-code), the
data that sets the analyzer to the correct parameters. A growing number of the
battery listings also include matrices to perform Cadex Quicktest™.
Point and click technology selects the battery and programs the Cadex 7000
Series analyzer. Scanning the battery’s model number, if a bar code label is
available, also programs the analyzer. Cadex Batteryshop™ supports up to
120 Cadex 7000 Series battery analyzers. The test results can be displayed on
screen in real time graphs and printed in customized reports.
Figure 18-5: The Cadex SM1 battery charger.
This charger accommodates the widely used
202 format. Other batteries that fit the bay are
the 2020, 1030, 1020, 210, 201, 36, 35, 30, 17
and 15. The Cadex SM1 charger supports
‘smart’ and ‘dumb’ batteries.
Cadex Smart Series battery chargers offer the consumer a continuous supply
of freshly charged batteries. Conforming to the SMBus Level 3, the Cadex
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Smart Series chargers accommodate Li-ion, NiMH and NiCd batteries. The
charge time is 2 to 3 hours. If faulty batteries are identified, the charge is
halted. On compatible footprint, the chargers also accommodate ‘dumb’
batteries. Typical uses are mobile computing, biomedical and survey devices.
The Cadex SM1 charger is compact and charges one battery at a time. The
Cadex SM2+ charger services two packs simultaneously and doubles as
conditioner and quality control system. The charger reads the data stored in
the SMBus battery, calculates the previous power delivered and compares the
results with the target capacity setting. Adjustable to 60, 70 and 80 percent,
the charger flags batteries that fall below the set capacity reading.
Figure 18-6: The Cadex SM2+ battery charger.
In addition to the features offered on the Cadex SM1 charger, this unit serves
as charger, quality control system and battery conditioner. SMBus batteries
with low state-of-health are identified. Conditioning and calibration occurs by
pressing a button.
Figure 18-7: Cadex UCC1, MCC2 and UCC6.
The Cadex UCC Series chargers feature interchangeable battery adapters. The
Cadex MCC2 serves both as desktop and mobile charger.
Cadex Universal Conditioning Chargers (UCC) offer battery users an
alternate source of chargers to those provided by the original equipment
manufacturer (OEM). Available in one, two and six bay configurations, the
chargers feature intelligent battery adapters. This concept allows easy
adaptation to a variety of battery types without compromising charge
performance.
The adapters allow service of different battery types in one unit.
Reconfiguration to other battery types can be done in the field; the one and
six-bay chargers are desktop and wall-mountable. The two-bay unit also
serves as a vehicular charger built to military shock and vibration
specifications.
Custom Battery Chargers — Cadex designs and manufactures a wide
variety of custom chargers to serve public safety, law enforcement,
emergency response, healthcare, mobile computing, broadcast and defence
applications. Cadex covers all aspects of product development, from circuit
design to power supply, from plastic housing to mechanical battery interface,
to testing and manufacturing.
Custom Battery Packs — Cadex completes the line of portable power source
by offering specialty battery packs. To provide added safety, Cadex has the
capability of designing specialty protection circuits for lithium ion chemistries
and other battery systems.
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Table of Contents | Battery FAQ | New Articles | About the Author | Links | Site Map
Copyright 2001 Isidor Buchmann. All rights reserved.
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